astronomy

second-biggest-black-hole-in-the-milky-way-found

Second-biggest black hole in the Milky Way found

astronomy, astrophysics, black holes, Gaia, Science, stars / /
A dark background with a bright point at the end of a curved path, and a small red circle.

Enlarge / The star’s orbit, shown here in light, is influenced by the far more massive black hole, indicated by the red orbit.

As far as black holes go, there are two categories: supermassive ones that live at the center of the galaxies (and we’re unsure about how they got there) and stellar mass ones that formed through the supernovae that end the lives of massive stars.

Prior to the advent of gravitational wave detectors, the heaviest stellar-mass black hole we knew about was only a bit more than a dozen times the mass of the Sun. And this makes sense, given that the violence of the supernova explosions that form these black holes ensures that only a fraction of the dying star’s mass gets transferred into its dark offspring. But then the gravitational wave data started flowing in, and we discovered there were lots of heavier black holes, with masses dozens of times that of the Sun. But we could only find them when they smacked into another black hole.

Now, thanks to the Gaia mission, we have observational evidence of the largest black hole in the Milky Way outside of the supermassive one, with a mass 33 times that of the Sun. And, in galactic terms, it’s right next door at about 2,000 light-years distant, meaning it will be relatively easy to learn more.

Mapping the stars

Although stellar-mass black holes are several times the mass of the Sun, they aren’t really all that heavy in the grand scheme of things. The sorts of stars that tend to leave black holes behind also tend to lead violent existences, spewing a lot of themselves into space before dying. And the supernova that forms the black hole obviously expels a lot of the star’s mass, rather than feeding it into the black hole. It had been thought that these processes set limits on how big a stellar mass black hole could be when it forms.

The discovery of larger black holes through gravitational wave detectors suggested that this wasn’t true. While there are ways for black holes to get bigger after they form—excessive feeding, mergers—it wasn’t clear that these events occurred often enough to explain the frequency of heavy black holes that we were seeing. And detecting them via gravitational waves doesn’t tell us anything about the history of how they got that large.

Which is why the discovery of Gaia BH3 (which is what the research team is using to avoid having to retype Gaia DR3 4318465066420528000 all the time) is so intriguing. The black hole is sitting calmly in a binary system, not doing anything in particular. But we know it’s there due to its gravitational influence.

Gaia is an ESA mission to map the location and movement of many of the Milky Way’s brighter stars by imaging them multiple times from different perspectives. It also gathers basic data on the stars’ light, allowing us to estimate things like age and composition. And, in addition to their movement across the galaxy, Gaia can measure their movement relative to Earth, a method that is useful for the detection of orbital interactions, such as the presence of companion stars or exoplanets.

The Gaia team was busy preparing for the fourth release of the data from the spacecraft and were running validation tests on the software used to detect binary star systems when they stumbled across Gaia BH3. While normally they’d publish its discovery at the same time as the data release, they consider the new object too important to wait: “We took the exceptional step of the publication of this paper based on preliminary data ahead of the official DR4 due to the unique nature of the discovery, which we believe should not be kept from the scientific community until the next release.”

Finding the invisible

Every star in our galaxy is in motion relative to every other. They orbit the center of our galaxy and may have a history that has imparted additional momentum—gravitational interactions with neighbors, having been part of a smaller galaxy that was consumed by the Milky Way, and so on. But that motion only changes on very long time scales. By contrast, any star in an orbit experiences regular changes in its motion in addition to its overall travel through the galaxy. As part of processing its data, the Gaia team attempts to identify both overall motion and any indications that a star is orbiting as part of a binary system.

The star that is orbiting Gaia BH3 is similar in mass to the Sun but shows the sort of periodic wobbles that indicate it’s in a mutual orbit with a companion. The companion itself, however, was completely invisible, which means it is almost certainly a black hole (the Gaia data had already been used to identify black holes this way). And, based on the mass and orbital motion of the visible star, it’s possible to estimate the mass of the invisible companion.

The estimate ended up being 32 solar masses, which is significantly larger than anything else identified in the Gaia dataset. So, the Gaia team wanted to confirm this wasn’t a software issue and used Earth-based telescopes to observe the same system. Three different observatories confirmed it was there, and the resulting mass estimates were slightly larger than those derived from the Gaia data alone: just under 33 solar masses.

Assuming it’s a single object and not two black holes orbiting each other closely, that makes it the largest non-supermassive black hole known in the Milky Way. And it places it in the mass range that had been difficult to explain via formations in supernovae.

Second-biggest black hole in the Milky Way found Read More »

a-supernova-caused-the-boat-gamma-ray-burst,-jwst-data-confirms

A supernova caused the BOAT gamma ray burst, JWST data confirms

astronomy, astrophysics, B.O.A.T., Gamma ray bursts, nucleosynthesis, Physics, Science, Webb telescope / /

Still the BOAT —

But astronomers are puzzled by the lack of signatures of expected heavy elements.

–

Artist's visualization of GRB 221009A showing the narrow relativistic jets — emerging from a central black hole — that gave rise to the brightest gamma ray burst yet detected.

Enlarge / Artist’s visualization of GRB 221009A showing the narrow relativistic jets—emerging from a central black hole—that gave rise to the brightest gamma-ray burst yet detected.

Aaron M. Geller/Northwestern/CIERA/ ITRC&DS

In October 2022, several space-based detectors picked up a powerful gamma-ray burst so energetic that astronomers nicknamed it the BOAT (Brightest Of All Time). Now they’ve confirmed that the GRB came from a supernova, according to a new paper published in the journal Nature Astronomy. However, they did not find evidence of heavy elements like platinum and gold one would expect from a supernova explosion, which bears on the longstanding question of the origin of such elements in the universe.

As we’ve reported previously, gamma-ray bursts are extremely high-energy explosions in distant galaxies lasting between mere milliseconds to several hours. There are two classes of gamma-ray bursts. Most (70 percent) are long bursts lasting more than two seconds, often with a bright afterglow. These are usually linked to galaxies with rapid star formation. Astronomers think that long bursts are tied to the deaths of massive stars collapsing to form a neutron star or black hole (or, alternatively, a newly formed magnetar). The baby black hole would produce jets of highly energetic particles moving near the speed of light, powerful enough to pierce through the remains of the progenitor star, emitting X-rays and gamma rays.

Those gamma-ray bursts lasting less than two seconds (about 30 percent) are deemed short bursts, usually emitting from regions with very little star formation. Astronomers think these gamma-ray bursts are the result of mergers between two neutron stars, or a neutron star merging with a black hole, comprising a “kilonova.” That hypothesis was confirmed in 2017 when the LIGO collaboration picked up the gravitational wave signal of two neutron stars merging, accompanied by the powerful gamma-ray bursts associated with a kilonova.

The October 2022 gamma-ray burst falls into the long category, lasting over 300 seconds. GRB 221009A triggered detectors aboard NASA’s Fermi Gamma-ray Space Telescope, the Neil Gehrels Swift Observatory, and Wind spacecraft, among others, just as gamma-ray astronomers had gathered for an annual meeting in Johannesburg, South Africa. The powerful signal came from the constellation Sagitta, traveling some 1.9 billion years to Earth.

Several papers were published last year reporting on the analytical results of all the observational data. Those findings confirmed that GRB 221009A was indeed the BOAT, appearing especially bright because its narrow jet was pointing directly at Earth. But the various analyses also yielded several surprising results that puzzled astronomers. Most notably, a supernova should have occurred a few weeks after the initial burst, but astronomers didn’t detect one, perhaps because it was very faint, and thick dust clouds in that part of the sky were dimming any incoming light.

Swift’s X-ray Telescope captured the afterglow of GRB 221009A about an hour after it was first detected.

Enlarge / Swift’s X-ray Telescope captured the afterglow of GRB 221009A about an hour after it was first detected.

NASA/Swift/A. Beardmore (University of Leicester)

That’s why Peter Blanchard of Northwestern University and his fellow co-authors decided to wait six months before undertaking their own analysis, relying on data collected during the GRB’s later phase by the Webb Space Telescope’s Near Infrared Spectrograph. They augmented that spectral data with observations from ALMA (Atacama Large Millimeter/Submillimeter Array) in Chile so they could separate light from the supernova and the GRB afterglow. The most significant finding was the telltale signatures of key elements like calcium and oxygen that one would expect to find with a supernova.

Yet the supernova wasn’t brighter than other supernovae associated with less energetic GRBs, which is puzzling. “You might expect that the same collapsing star producing a very energetic and bright GRB would also produce a very energetic and bright supernova,” said Blanchard. “But it turns out that’s not the case. We have this extremely luminous GRB, but a normal supernova.” The authors suggest that this might have something to do with the shape and structure of the relativistic jet, which was much narrower than other GRB jets, resulting in a more focused and brighter beam of light.

The data held another surprise for astronomers. The only confirmed source of heavy elements in the universe to date is the merging of binary neutron stars. But per Blanchard, there are far too few neutron star mergers to account for the abundance of heavy elements, so there must be another source. One hypothetical additional source is a rapidly spinning massive star that collapses and explodes into a supernova. Alas, there was no evidence of heavy elements in the JWST spectral data regarding the BOAT.

“When we confirmed that the GRB was generated by the collapse of a massive star, that gave us the opportunity to test a hypothesis for how some of the heaviest elements in the universe are formed,” said Blanchard. “We did not see signatures of these heavy elements, suggesting that extremely energetic GRBs like the BOAT do not produce these elements. That doesn’t mean that all GRBs do not produce them, but it’s a key piece of information as we continue to understand where these heavy elements come from. Future observations with JWST will determine if the BOAT’s ‘normal’ cousins produce these elements.”

Nature Astronomy, 2024. DOI: 10.1038/s41550-024-02237-4  (About DOIs).

A supernova caused the BOAT gamma ray burst, JWST data confirms Read More »

mars-may-not-have-had-liquid-water-long-enough-for-life-to-form

Mars may not have had liquid water long enough for life to form

astronomy, carbon dioxide, Mars, planetary science, Science, water / /

Subliminal —

Lab experiments suggest gullies on Mars might form when carbon dioxide heats up.

–

Image of a grey-colored slope with channels cut into it.

Mars has a history of liquid water on its surface, including lakes like the one that used to occupy Jezero Crater, which have long since dried up. Ancient water that carried debris—and melted water ice that presently does the same—were also thought to be the only thing driving the formation of gullies spread throughout the Martian landscape. That view may now change thanks to new results that suggest dry ice can also shape the landscape.

It’s sublime

Previously, scientists were convinced that only liquid water shaped gullies on Mars because that’s what happens on Earth. What was not taken into account was sublimation, or the direct transition of a substance from a solid to a gaseous state. Sublimation is how CO2 ice disappears (sometimes water ice experiences this, too).

Frozen carbon dioxide is everywhere on Mars, including in its gullies. When CO2 ice sublimates on one of these gullies, the resulting gas can push debris further down the slope and continue to shape it.

Led by planetary researcher Lonneke Roelofs of Utrecht University in the Netherlands, a team of scientists has found that the sublimation of CO2 ice could have shaped Martian gullies, which might mean the most recent occurrence of liquid water on Mars may have been further back in time than previously thought. That could also mean the window during which life could have emerged and thrived on Mars was possibly smaller.

“Sublimation of CO2 ice, under Martian atmospheric conditions, can fluidize sediment and creates morphologies similar to those observed on Mars,” Roelofs and her colleagues said in a study recently published in Communications Earth & Environment.

Into thin air

Earth and Martian gullies have basically the same morphology. The difference is that we’re certain that liquid water is behind their formation and continuous shaping and re-shaping on Earth. Such activity includes new channels being carved out and more debris being taken to the bottom.

While ancient Mars may have had enough stable liquid water to pull this off, there is not enough on the present surface of Mars to sustain that kind of activity. This is where sublimation comes in. CO2 ice has been observed on the surface of Mars at the same time that material starts flowing.

After examining observations like these, the researchers hypothesized these flows are pushed downward by gas as the frozen carbon dioxide sublimates. Because of the low pressure on Mars, sublimation creates a relatively greater gas flux than it would on Earth—enough power to make fluid motion of material possible.

There are two ways sublimation can be triggered to get these flows moving. When part of a more exposed area of a gully collapses, especially on a steep slope, sediment and other debris that have been warmed by the Sun can fall on CO2 ice in a shadier and cooler area. Heat from the falling material could supply enough energy for the frost to sublimate. Another possibility is that CO2 ice and sediment can break from the gully and fall onto warmer material, which will also trigger sublimation.

Mars in a lab

There is just one problem with these ideas: since humans have not landed on Mars (yet), there are no in situ observations of these phenomena, only images and data beamed back from spacecraft. So, everything is hypothetical. The research team would have to model Martian gullies to watch the action in real time.

To re-create a part of the red planet’s landscape in a lab, Roelofs built a flume in a special environmental chamber that simulated the atmospheric pressure of Mars. It was steep enough for material to move downward and cold enough for CO2 ice to remain stable. But the team also added warmer adjacent slopes to provide heat for sublimation, which would drive movement of debris. They experimented with both scenarios that might happen on Mars: heat coming from beneath the CO2 ice and warm material being poured on top of it. Both produced the kinds of flows that had been hypothesized.

For further evidence that flows driven by sublimation would happen under certain conditions, two further experiments were conducted, one under Earth-like pressures and one without CO2 ice. No flows were produced by either.

“For the first time, these experiments provide direct evidence that CO2 sublimation can fluidize, and sustain, granular flows under Martian atmospheric conditions,” the researchers said in the study.

Because this experiment showed that gullies and systems like them can be shaped by sublimation and not just liquid water, it raises questions about how long Mars had a sufficient supply of liquid water on the surface for any organisms (if they existed at all) to survive. Its period of habitability might have been shorter than it was once thought to be. Does this mean nothing ever lived on Mars? Not necessarily, but Roelofs’ findings could influence how we see planetary habitability in the future.

Communications Earth & Environment, 2024. DOI: 10.1038/s43247-024-01298-7

Mars may not have had liquid water long enough for life to form Read More »

the-best-robot-to-search-for-life-could-look-like-a-snake

The best robot to search for life could look like a snake

astrobiology, astronomy, Biology, Enceladus, planetary science, Robots, Science / /
Image of two humans sitting behind a control console dressed in heavy clothing, while a long tube sits on the ice in front of them.

Enlarge / Trying out the robot on a glacier.

Icy ocean worlds like Europa or Enceladus are some of the most promising locations for finding extra-terrestrial life in the Solar System because they host liquid water. But to determine if there is something lurking in their alien oceans, we need to get past ice cover that can be dozens of kilometers thick. Any robots we send through the ice would have to do most of the job on their own because communication with these moons takes as much as 155 minutes.

Researchers working on NASA Jet Propulsion Laboratory’s technology development project called Exobiology Extant Life Surveyor (EELS) might have a solution to both those problems. It involves using an AI-guided space snake robot. And they actually built one.

Geysers on Enceladus

The most popular idea to get through the ice sheet on Enceladus or Europa so far has been thermal drilling, a technique used for researching glaciers on Earth. It involves a hot drill that simply melts its way through the ice. “Lots of people work on different thermal drilling approaches, but they all have a challenge of sediment accumulation, which impacts the amount of energy needed to make significant progress through the ice sheet,” says Matthew Glinder, the hardware lead of the EELS project.

So, instead of drilling new holes in ice, the EELS team focuses on using ones that are already there. The Cassini mission discovered geyser-like jets shooting water into space from vents in the ice cover near Enceladus’ south pole. “The concept was you’d have a lander to land near a vent and the robot would move on the surface and down into the vent, search the vent, and through the vent go further down into the ocean”, says Matthew Robinson, the EELS project manager.

The problem was that the best Cassini images of the area where that lander would need to touch down have a resolution of roughly 6 meters per pixel, meaning major obstacles to landing could be undetected. To make things worse, those close-up images were monocular, which meant we could not properly figure out the topography. “Look at Mars. First we sent an orbiter. Then we sent a lander. Then we sent a small robot. And then we sent a big robot. This paradigm of exploration allowed us to get very detailed information about the terrain,” says Rohan Thakker, the EELS autonomy lead. “But it takes between seven to 11 years to get to Enceladus. If we followed the same paradigm, it would take a century,” he adds.

All-terrain snakes

To deal with unknown terrain, the EELS team built a robot that could go through almost anything—a versatile, bio-inspired, snake-like design about 4.4 meters long and 35 centimeters in diameter. It weighs about 100 kilograms (on Earth, at least). It’s made of 10 mostly identical segments. “Each of those segments share a combination of shape actuation and screw actuation that rotates the screws fitted on the exterior of the segments to propel the robot through its environment,” explains Glinder. By using those two types of actuators, the robot can move using what the team calls “skin propulsion,” which relies on the rotation of screws, or using one of various shape-based movements that rely on shape actuators. “Sidewinding is one of those gaits where you are just pressing the robot against the environment,” Glinder says.

The basic design also works on surfaces other than ice.

Enlarge / The basic design also works on surfaces other than ice.

The standard sensor suite is fitted on the head and includes a set of stereo cameras providing a 360-degree viewing angle. There are also inertial measuring units (IMUs) that use gyroscopes to estimate the robot’s position, and lidar sensors. But it also has a sense of touch. “We are going to have torque force sensors in each segment. This way we will have direct torque plus direct force sensing at each joint,” explains Robinson. All this is supposed to let the EELS robot safely climb up and down Enceladus’ vents, hold in place in case of eruptions by pressing itself against the walls, and even navigate by touch alone if cameras and lidar don’t work.

But perhaps the most challenging part of building the EELS robot was its brain.

The best robot to search for life could look like a snake Read More »

astronomers-have-solved-the-mystery-of-why-this-black-hole-has-the-hiccups

Astronomers have solved the mystery of why this black hole has the hiccups

astronomy, astrophysics, black holes, Physics, Science / /

David vs. Goliath —

Blame it on a smaller orbiting black hole repeatedly punching through the accretion disk.

–

graphic of hiccuping black hole

Enlarge / Scientists have found a large black hole that “hiccups,” giving off plumes of gas.

Jose-Luis Olivares, MIT

In December 2020, astronomers spotted an unusual burst of light in a galaxy roughly 848 million light-years away—a region with a supermassive black hole at the center that had been largely quiet until then. The energy of the burst mysteriously dipped about every 8.5 days before the black hole settled back down, akin to having a case of celestial hiccups.

Now scientists think they’ve figured out the reason for this unusual behavior. The supermassive black hole is orbited by a smaller black hole that periodically punches through the larger object’s accretion disk during its travels, releasing a plume of gas. This suggests that black hole accretion disks might not be as uniform as astronomers thought, according to a new paper published in the journal Science Advances.

Co-author Dheeraj “DJ” Pasham of MIT’s Kavli Institute for Astrophysics and Space research noticed the community alert that went out after the All Sky Automated Survey for SuperNovae (ASAS-SN) detected the flare, dubbed ASASSN-20qc. He was intrigued and still had some allotted time on the X-ray telescope, called NICER (the Neutron star Interior Composition Explorer) on board the International Space Station. He directed the telescope to the galaxy of interest and gathered about four months of data, after which the flare faded.

Pasham noticed a strange pattern as he analyzed that four months’ worth of data. The bursts of energy dipped every 8.5 days in the X-ray regime, much like a star’s brightness can briefly dim whenever an orbiting planet crosses in front. Pasham was puzzled as to what kind of object could cause a similar effect in an entire galaxy. That’s when he stumbled across a theoretical paper by Czech physicists suggesting that it was possible for a supermassive black hole at the center of a galaxy to have an orbiting smaller black hole; they predicted that, under the right circumstances, this could produce just such a periodic effect as Pasham had observed in his X-ray data.

Computer simulation of an intermediate-mass black hole orbiting a supermassive black hole and driving periodic gas plumes that can explain the observations.

Computer simulation of an intermediate-mass black hole orbiting a supermassive black hole and driving periodic gas plumes that can explain the observations.

Petra Sukova, Astronomical Institute of the CAS

“I was super excited about this theory and immediately emailed to say, ‘I think we’re observing exactly what your theory predicted,” Pasham said. They joined forces to run simulations incorporating the data from NICER, and the results supported the theory. The black hole at the galaxy’s center is estimated to have a mass of 50 million suns. Since there was no burst before December 2020, the team thinks there was, at most, just a faint accretion disk around that black hole and a smaller orbiting black hole of between 100 to 10,000 solar masses that eluded detection because of that.

So what changed? Pasham et al. suggest that a nearby star got caught in the gravitational pull of the supermassive black hole in December 2020 and was ripped to shreds, known as a tidal disruption event (TDE). As previously reported, in a TDE, part of the shredded star’s original mass is ejected violently outward. This, in turn, can form an accretion disk around the black hole that emits powerful X-rays and visible light. The jets are one way astronomers can indirectly infer the presence of a black hole. Those outflow emissions typically occur soon after the TDE.

That seems to be what happened in the current system to cause the sudden flare in the primary supermassive black hole. Now it had a much brighter accretion disk, so when its smaller black hole partner passed through the disk, larger than usual gas plumes were emitted. As luck would have it, that plume just happened to be pointed in the direction of an observing telescope.

Astronomers have known about so-called “David and Goliath” binary black hole systems for a while, but “this is a different beast,” said Pasham. “It doesn’t fit anything that we know about these systems. We’re seeing evidence of objects going in and through the disk, at different angles, which challenges the traditional picture of a simple gaseous disk around black holes. We think there is a huge population of these systems out there.”

Science Advances, 2024. DOI: 10.1126/sciadv.adj8898  (About DOIs).

Astronomers have solved the mystery of why this black hole has the hiccups Read More »

event-horizon-telescope-captures-stunning-new-image-of-milky-way’s-black-hole

Event Horizon Telescope captures stunning new image of Milky Way’s black hole

astronomy, astrophysics, black holes, Event Horizon Telescope, Physics, Science / /
A new image from the Event Horizon Telescope has revealed powerful magnetic fields spiraling from the edge of a supermassive black hole at the center of the Milky Way, Sagittarius A*.

Enlarge / A new image from the Event Horizon Telescope has revealed powerful magnetic fields spiraling from the edge of a supermassive black hole at the center of the Milky Way, Sagittarius A*.

EHT Collaboration

Physicists have been confident since the1980s that there is a supermassive black hole at the center of the Milky Way galaxy, similar to those thought to be at the center of most spiral and elliptical galaxies. It’s since been dubbed Sagittarius A* (pronounced A-star), or SgrAfor short. The Event Horizon Telescope (EHT) captured the first image of SgrAtwo years ago. Now the collaboration has revealed a new polarized image (above) showcasing the black hole’s swirling magnetic fields. The technical details appear in two new papers published in The Astrophysical Journal Letters. The new image is strikingly similar to another EHT image of a larger supermassive black hole, M87*, so this might be something that all such black holes share.

The only way to “see” a black hole is to image the shadow created by light as it bends in response to the object’s powerful gravitational field. As Ars Science Editor John Timmer reported in 2019, the EHT isn’t a telescope in the traditional sense. Instead, it’s a collection of telescopes scattered around the globe. The EHT is created by interferometry, which uses light in the microwave regime of the electromagnetic spectrum captured at different locations. These recorded images are combined and processed to build an image with a resolution similar to that of a telescope the size of the most distant locations. Interferometry has been used at facilities like ALMA (the Atacama Large Millimeter/submillimeter Array) in northern Chile, where telescopes can be spread across 16 km of desert.

In theory, there’s no upper limit on the size of the array, but to determine which photons originated simultaneously at the source, you need very precise location and timing information on each of the sites. And you still have to gather sufficient photons to see anything at all. So atomic clocks were installed at many of the locations, and exact GPS measurements were built up over time. For the EHT, the large collecting area of ALMA—combined with choosing a wavelength in which supermassive black holes are very bright—ensured sufficient photons.

In 2019, the EHT announced the first direct image taken of a black hole at the center of an elliptical galaxy, Messier 87, located in the constellation of Virgo some 55 million light-years away. This image would have been impossible a mere generation ago, and it was made possible by technological breakthroughs, innovative new algorithms, and (of course) connecting several of the world’s best radio observatories. The image confirmed that the object at the center of M87is indeed a black hole.

In 2021, the EHT collaboration released a new image of M87showing what the black hole looks like in polarized light—a signature of the magnetic fields at the object’s edge—which yielded fresh insight into how black holes gobble up matter and emit powerful jets from their cores. A few months later, the EHT was back with images of the “dark heart” of a radio galaxy known as Centaurus A, enabling the collaboration to pinpoint the location of the supermassive black hole at the galaxy’s center.

SgrAis much smaller but also much closer than M87*. That made it a bit more challenging to capture an equally sharp image because SgrAchanges on time scales of minutes and hours compared to days and weeks for M87*. Physicist Matt Strassler previously compared the feat to “taking a one-second exposure of a tree on a windy day. Things get blurred out, and it can be difficult to determine the true shape of what was captured in the image.”

Event Horizon Telescope captures stunning new image of Milky Way’s black hole Read More »

this-rare-11th-century-islamic-astrolabe-is-one-of-the-oldest-yet-discovered

This rare 11th-century Islamic astrolabe is one of the oldest yet discovered

astrolabes, astronomy, history of science, Science / /

An instrument from Verona —

“A powerful record of scientific exchange between Arabs, Jews, & Christians over 100s of years.”

–

Close up of the Verona astrolabe showing Hebrew inscribed (top left) above Arabic inscriptions

Enlarge / Close-up of the 11th-century Verona astrolabe showing Hebrew (top left) and Arabic inscriptions.

Federica Gigante

Cambridge University historian Federica Gigante is an expert on Islamic astrolabes. So naturally she was intrigued when the Fondazione Museo Miniscalchi-Erizzo in Verona, Italy, uploaded an image of just such an astrolabe to its website. The museum thought it might be a fake, but when Gigante visited to see the astrolabe firsthand, she realized it was not only an authentic 11th-century instrument—one of the oldest yet discovered—it had engravings in both Arabic and Hebrew.

“This isn’t just an incredibly rare object. It’s a powerful record of scientific exchange between Arabs, Jews, and Christians over hundreds of years,” Gigante said. “The Verona astrolabe underwent many modifications, additions, and adaptations as it changed hands. At least three separate users felt the need to add translations and corrections to this object, two using Hebrew and one using a Western language.” She described her findings in a new paper published in the journal Nuncius.

As previously reported, astrolabes are actually very ancient instruments—possibly dating as far back as the second century BCE—for determining the time and position of the stars in the sky by measuring a celestial body’s altitude above the horizon. Before the emergence of the sextant, astrolabes were mostly used for astronomical and astrological studies, although they also proved useful for navigation on land, as well as for tracking the seasons, tide tables, and time of day. The latter was especially useful for religious functions, such as tracking daily Islamic prayer times, the direction of Mecca, or the feast of Ramadan, among others.

Navigating at sea on a pitching deck was a bit more problematic unless the waters were calm. The development of a mariner’s astrolabe—a simple ring marked in degrees for measuring celestial altitudes—helped solve that problem. It was eventually replaced by the invention of the sextant in the 18th century, which was much more precise for seafaring navigation. Mariners’ astrolabes are among the most prized artifacts recovered from shipwrecks; only 108 are currently cataloged worldwide. In 2019, researchers determined that a mariner’s astrolabe recovered from the wreck of one of Portuguese explorer Vasco da Gama’s ships is now officially the oldest known such artifact. The so-called Sodré astrolabe was recovered from the wreck of the Esmeralda (part of da Gama’s armada) off the coast of Oman in 2014, along with around 2,800 other artifacts.

An astrolabe is typically composed of a disk (mater) engraved with graduations to mark hours and/or arc degrees. The mater holds one more engraved flat plate (tympans) to represent azimuth and altitude at specific latitudes. Above these pieces is a rotating framework called the rete that essentially serves as a star map, with one rotation being equivalent to one day. An alidade attached to the back could be rotated to help the user take the altitude of a sighted star. Engravings on the backs of the astrolabes varied but often depicted different kinds of scales.

  • The Verona astrolabe, front and back views.

    Federica Gigante

  • Close-up of the Verona astrolabe showing inscribed Hebrew, Arabic, and Western numerals.

    Federica Gigante

  • Dedication and signature: “For Isḥāq […], the work of Yūnus.”

    Federica Gigante

  • Federica Gigante examining the Verona astrolabe.

    Federica Candelato

The Verona astrolabe is meant for astronomical use, and while it has a mater, a rete, and two plates (one of which is a later replacement), it is missing the alidade. It’s also undated, according to Gigante, but she was able to estimate a likely date based on the instrument’s design, construction, and calligraphy. She concluded it was Andalusian, dating back to the 11th century when the region was a Muslim-ruled area of Spain.

For instance, one side of the original plate bears an Arabic inscription “for the latitude of Cordoba, 38° 30′,” and another Arabic inscription on the other side reads “for the latitude of Toledo, 40°.” The second plate (added at some later date) was for North African latitudes, so at some point, the astrolabe might have found its way to Morocco or Egypt. There are engraved lines from Muslim prayers, indicating it was probably originally used for daily prayers.

There is also a signature on the back in Arabic script: “for Isḥāq […]/the work of Yūnus.” Gigante believes this was added by a later owner. Since the two names translate to Isaac and Jonah, respectively, in English, it’s possible that a later owner was an Arab-speaking member of a Sephardi Jewish community. In addition to the Arabic script, Gigante noticed later Hebrew inscriptions translating the Arabic names for certain astrological signs, in keeping with the earliest surviving treatise in Hebrew on astrolabes, written by Abraham Ibn Ezra in Verona in 1146.

“These Hebrew additions and translations suggest that at a certain point the object left Spain or North Africa and circulated amongst the Jewish diaspora community in Italy, where Arabic was not understood, and Hebrew was used instead,” said Gigante. “This object is Islamic, Jewish, and European, they can’t be separated.”

Nuncius, 2024. DOI: 10.1163/18253911-bja10095  (About DOIs).

This rare 11th-century Islamic astrolabe is one of the oldest yet discovered Read More »

newly-spotted-black-hole-has-mass-of-17-billion-suns,-adding-another-daily

Newly spotted black hole has mass of 17 billion Suns, adding another daily

accretion disk, astronomy, astrophysics, black hole, quasar, Science, supermassive black hole / /

Feeding frenzy —

An accretion disk 7 light-years across powers an exceptionally bright galaxy.

–

Artist's view of a tilted orange disk with a black object at its center.

Quasars initially confused astronomers when they were discovered. First identified as sources of radio-frequency radiation, later observations showed that the objects had optical counterparts that looked like stars. But the spectrum of these ostensible stars showed lots of emissions at wavelengths that didn’t seem to correspond to any atoms we knew about.

Eventually, we figured out these were spectral lines of normal atoms but heavily redshifted by immense distances. This means that to appear like stars at these distances, these objects had to be brighter than an entire galaxy. Eventually, we discovered that quasars are the light produced by an actively feeding supermassive black hole at the center of a galaxy.

But finding new examples has remained difficult because, in most images, they continue to look just like stars—you still need to obtain a spectrum and figure out their distance to know you’re looking at a quasar. Because of that, there might be some unusual quasars we’ve ignored because we didn’t realize they were quasars. That’s the case with an object named J0529−4351, which turned out to be the brightest quasar we’ve ever observed.

That’s no star!

J0529−4351 had been observed a number of times, but its nature wasn’t recognized until a survey went hunting for quasars and recognized it was one. At the time of the 2023 paper that described the survey, the researchers behind it suggested that it had either been magnified through gravitational lensing, or it was the brightest quasar we’ve ever identified.

In this week’s Nature Astronomy, they confirmed: It’s not lensed, it really is that bright. Gravitational lensing tends to distort objects or create multiple images of them. But J0529−4351 is undistorted, and nothing nearby looks like it. And there’s nothing in the foreground that has enough mass to create a lens.

So, how do you take an instance of an incredibly bright object and make it even brighter? The light from a quasar is produced by an accretion disk. While accretion disks can form around black holes with masses similar to stars, quasars require a supermassive black hole like the ones found at the center of galaxies. These disks are formed of material that has been captured by the gravity of the black hole and is in orbit before falling inward and crossing the event horizon. Light is created as the material is heated by collisions of its constituent particles and gives up gravitational energy as it falls inward.

Getting more light out of an accretion disk is pretty simple: You either put more material in it or make it bigger. But there’s a limit to how much material you can cram into one. At some point, the accretion disk will produce so much radiation that it drives off any additional material that’s falling inward, essentially choking off its own food supply. Called the Eddington limit, this sets ceilings on how bright an accretion disk can be and how quickly a black hole can grow.

Factors like the mass of the black hole and its spin help set the Eddington limit. Plus, the amount of material falling inward can drop below the Eddington limit, leading to a bit less light being produced. Trying various combinations of these factors and checking them against observational data, the researchers came up with several estimates for the properties of the supermassive black hole and its accretion disk.

Extremely bright

For the supermassive black hole’s size, the researchers propose two possible estimates: one at 17 billion solar masses, and the other at 19 billion solar masses. That’s not the most massive one known, but there are only about a dozen thought to be larger. (For comparison, the one at the center of the Milky Way is “only” about 4 million solar masses.) The data is best fit by a moderate spin, with us viewing it from about 45 degrees off the pole of the black hole. The accretion disk would be roughly seven light-years across. Meaning, if the system were centered on our Sun, several nearby stars would be within the disk.

The accretion rate needed to power the brightness is just below the Eddington limit and works out to roughly 370 solar masses of material per year. Or, about a Sun a day. At that rate, it would take about 30 million years to double in size.

But it’s rare to have that much material around for one to feed that long. And a look through archival images shows that the brightness of J0529−4351 can vary by as much as 15 percent, so it’s not likely to be pushing the Eddington limit the entire time.

Even so, it’s difficult to understand how that much material can be driven into the center of a galaxy for any considerable length of time. The researchers suggest that the ALMA telescope array might be able to pick up anything unusual there. “If extreme quasars were caused by unusual host galaxy gas flows, ALMA should see this,” they write. “If nothing unusual was found in the host gas, then this would sharpen the well-known puzzle of how to sustain high accretion rates for long enough to form such extreme supermassive black holes.”

The whole accretion disk is also large enough that it should be possible to image it with the Very Large Telescope, which would allow us to track the disk’s rotation and estimate the black hole’s mass.

The system’s extreme nature, then, may actually help us figure out its details despite its immense distance. Meanwhile, the researchers wonder whether other unusual systems might remain undiscovered simply because we haven’t considered that an object might be a quasar instead of a star.

Nature Astronomy, 2024. DOI: 10.1038/s41550-024-02195-x  (About DOIs).

Newly spotted black hole has mass of 17 billion Suns, adding another daily Read More »

new-app-always-points-to-the-supermassive-black-hole-at-the-center-of-our-galaxy

New app always points to the supermassive black hole at the center of our galaxy

AI, astronomy, Biz & IT, chatgpt, chatgtp, Galactic Center, Galactic Compass, machine learning, Matt Webb, Space, Tech / /

the final frontier —

iPhone compass app made with AI assistance locates the heart of the Milky Way.

–

A photo of Galactic Compass running on an iPhone.

Enlarge / A photo of Galactic Compass running on an iPhone.

Matt Webb / Getty Images

On Thursday, designer Matt Webb unveiled a new iPhone app called Galactic Compass, which always points to the center of the Milky Way galaxy—no matter where Earth is positioned on our journey through the stars. The app is free and available now on the App Store.

While using Galactic Compass, you set your iPhone on a level surface, and a big green arrow on the screen points the way to the Galactic Center, which is the rotational core of the spiral galaxy all of us live in. In that center is a supermassive black hole known as Sagittarius A*, a celestial body from which no matter or light can escape. (So, in a way, the app is telling us what we should avoid.)

But truthfully, the location of the galactic core at any given time isn’t exactly useful, practical knowledge—at least for people who aren’t James Tiberius Kirk in Star Trek V. But it may inspire a sense of awe about our place in the cosmos.

Screenshots of Galactic Compass in action, captured by Ars Technica in a secret location.

Enlarge / Screenshots of Galactic Compass in action, captured by Ars Technica in a secret location.

Benj Edwards / Getty Images

“It is astoundingly grounding to always have a feeling of the direction of the center of the galaxy,” Webb told Ars Technica. “Your perspective flips. To begin with, it feels arbitrary. The middle of the Milky Way seems to fly all over the sky, as the Earth turns and moves in its orbit.”

Webb’s journey to creating Galactic Compass began a decade ago as an offshoot of his love for casual astronomy. “About 10 years ago, I taught myself how to point to the center of the galaxy,” Webb said. “I lived in an apartment where I had a great view of the stars, so I was using augmented reality apps to identify them, and I gradually learned my way around the sky.”

While Webb initially used an astronomy app to help locate the Galactic Center, he eventually taught himself how to always find it. He described visualizing himself on the surface of the Earth as it spins and tilts, understanding the ecliptic as a line across the sky and recognizing the center of the galaxy as an invisible point moving predictably through the constellation Sagittarius, which lies on the ecliptic line. By visualizing Earth’s orbit over the year and determining his orientation in space, he was able to point in the right direction, refining his ability through daily practice and comparison with an augmented reality app.

With a little help from AI

Our galaxy, the Milky Way, is thought to look similar to Andromeda (seen here) if you could see it from a distance. But since we're inside the galaxy, all we can see is the edge of the galactic plane.

Enlarge / Our galaxy, the Milky Way, is thought to look similar to Andromeda (seen here) if you could see it from a distance. But since we’re inside the galaxy, all we can see is the edge of the galactic plane.

Getty Images

In 2021, Webb imagined turning his ability into an app that would help take everyone on the same journey, showing a compass that points toward the galactic center instead of Earth’s magnetic north. “But I can’t write apps,” he said. “I’m a decent enough engineer, and an amateur designer, but I’ve never figured out native apps.”

That’s where ChatGPT comes in, transforming Webb’s vision into reality. With the AI assistant as his coding partner, Webb progressed step by step, crafting a simple app interface and integrating complex calculations for locating the galactic center (which involves calculating the user’s azimuth and altitude).

Still, coding with ChatGPT has its limitations. “ChatGPT is super smart, but it’s not embodied like a human, so it falls down on doing the 3D calculations,” he says. “I had to learn a lot about quaternions, which are a technique for combining 3D rotations, and even then, it’s not perfect. The app needs to be held flat to work simply because my math breaks down when the phone is upright! I’ll fix this in future versions,” Webb said.

Webb is no stranger to ChatGPT-powered creations that are more fun than practical. Last month, he launched a Kickstarter for an AI-rhyming poetry clock called the Poem/1. With his design studio, Acts Not Facts, Webb says he uses “whimsy and play to discover the possibilities in new technology.”

Whimsical or not, Webb insists that Galactic Compass can help us ponder our place in the vast universe, and he’s proud that it recently peaked at #87 in the Travel chart for the US App Store. In this case, though, it’s spaceship Earth that is traveling the galaxy while every living human comes along for the ride.

“Once you can follow it, you start to see the galactic center as the true fixed point, and we’re the ones whizzing and spinning. There it remains, the supermassive black hole at the center of our galaxy, Sagittarius A*, steady as a rock, eternal. We go about our days; it’s always there.”

New app always points to the supermassive black hole at the center of our galaxy Read More »

webb-telescope-spots-hints-that-eris,-makemake-are-geologically-active

Webb telescope spots hints that Eris, Makemake are geologically active

astronomy, dwarf planet, Eris, geology, Kuiper belt, Makemake, planetary science, Science / /
Image of two small planets, one more reddish, the second very white.

Enlarge / Artist’s conceptions of what the surfaces of two dwarf planets might look like.

Active geology—and the large-scale chemistry it can drive—requires significant amounts of heat. Dwarf planets near the far edges of the Solar System, like Pluto and other Kuiper Belt objects, formed from frigid, icy materials and have generally never transited close enough to the Sun to warm up considerably. Any heat left over from their formation was likely long since lost to space.

Yet Pluto turned out to be a world rich in geological features, some of which implied ongoing resurfacing of the dwarf planet’s surface. Last week, researchers reported that the same might be true for other dwarf planets in the Kuiper Belt. Indications come thanks to the capabilities of the Webb telescope, which was able to resolve differences in the hydrogen isotopes found on the chemicals that populate the surface of Eris and Makemake.

Cold and distant

Kuiper Belt objects are natives of the distant Solar System, forming far enough from the warmth of the Sun that many materials that are gasses in the inner planets—things like nitrogen, methane, and carbon dioxide—are solid ices. Many of these bodies formed far enough from the gravitational influence of the eight major planets that they have never made a trip into the warmer inner Solar System. In addition, because there was much less material that far from the Sun, most of the bodies are quite small.

While they would have started off hot due to the process by which they formed, their small size means a large surface-to-volume ratio, allowing internal heat to radiate out to space relatively quickly. Since then, any heat has come from rare collision events or the decay of radioactive isotopes.

Yet New Horizons’ visit to Pluto made it clear that it doesn’t take much heat to drive active geology, although seasonal changes in sunlight are likely to account for some of its features. Sunlight is less likely to be an influence for worlds like Makemake, which orbits at a distance one and a half times Pluto’s closest approach to the Sun. Eris, which is nearly as large as Pluto, orbits at over twice Pluto’s closest approach.

Sending a mission to either of these planets would take decades, and none are in development at the moment, so we can’t know what their surfaces look like. But that doesn’t mean we know nothing about them. And the James Webb Space Telescope has added to what we know considerably.

The Webb was used to image sunlight reflected off these objects, obtaining its infrared spectrum—the amount of light reflected at different wavelengths. The spectrum is influenced by the chemical composition of the dwarf planets’ surfaces. Certain chemicals can absorb specific wavelengths of infrared light, ensuring they don’t get reflected. By noting where the spectrum dips, it’s possible to figure out which chemicals are present.

Some of that work has already been done. But Webb is able to image parts of the spectrum that were inaccessible earlier, and its instruments are even able to identify different isotopes of the atoms composing each chemical. For example, some molecules of methane (CH4) will, at random, have one of their hydrogen atoms swapped out for its heavier isotope, deuterium, forming CH3D. These isotopes can potentially act as tracers, telling us things about where the chemicals originally came from.

Webb telescope spots hints that Eris, Makemake are geologically active Read More »

ligo-goes-to-space:-esa-to-proceed-with-lisa-gravitational-wave-detector

LIGO goes to space: ESA to proceed with LISA gravitational wave detector

astronomy, cosmology, ESA, gravitational waves, LIGO, Lisa, Science, Space / /

Let’s go LISA —

A gravitational wave detector in space will be sensitive to unexplored phenomena.

–

Image of three spacecraft with red lines connecting them.

Enlarge / The LISA project will consist of three spacecraft in a triangular configuration, exchanging lasers.

On Thursday, the European Space Agency’s Science Programme Committee gave the go-ahead to the Laser Interferometer Space Antenna, or LISA project. This would mean the construction of the mission’s three spacecraft could begin as early as a year from now. While the interferometer would follow the same basic principles as the ground-based LIGO (Laser Interferometer Gravitational-Wave Observatory) experiment that first detected gravitational waves, the hardware would be placed 2.5 million kilometers apart, making it sensitive to an entirely new range of astronomical phenomena.

Proven tech

Existing gravitational wave detectors rely on bouncing lasers back and forth between distant mirrors before recombining them to produce an interference pattern. Anything that alters the position of the mirrors—from the rumble of a large truck to the passing of gravitational waves—will change the interference pattern. Having detectors at distant sites helps us eliminate cases of local noise, allowing us to detect astronomical events.

The detectors we’ve built on Earth have successfully picked up gravitational waves generated by the mergers of compact objects like neutron stars and black holes. But their relatively compact size means that they can only capture high-frequency gravitational waves, which are only produced in the last few seconds before a merger takes place.

To capture more of the process, we need to detect low-frequency gravitational waves. And that means a much larger distance between the interferometer’s mirrors and an escape from the seismic noise of Earth. It means going to space.

The LISA design consists of an outer shell of a spacecraft that absorbs the jostling of the dust and cosmic rays that tear through our Solar System and powers a laser strong enough to reach 2.5 million kilometers. It will also house a telescope to focus incoming laser light, which will spread from its normal tight beam over these distances. Floating freely within is a mass that, isolated from the rest of the Universe, should provide a stable platform to pick up any changes in the laser. Three spacecraft trail the Earth in its orbit around the Sun, each sending lasers to two others in a triangular configuration.

That may sound like science fiction, but ESA has already sent a pathfinder mission to space to test the technology. And it performed 20 times better than planned, providing three times the sensitivity needed for LISA to work. So there’s no obvious sticking point.

Going supermassive

Once it gets to space, it should immediately pick up the impending collisions that have resulted in LIGO detections. But it will spot them as much as a full year in advance and allow us to track where the event horizons touch. This would allow us to track the physics of their interactions over time and to potentially point optical telescopes in the right direction ahead of collisions so that we can determine whether any of these events produce radiation. (This may allow us to assign causes to some classes of events we’ve already detected via the photons.)

But that’s only part of the benefit. Due to their far larger size, supermassive black hole mergers are only detectable at lower frequencies. Since these are expected to happen following many galaxy mergers, it’s hoped we’ll be able to capture them.

Perhaps the most exciting prospect is that LISA could pick up the early gravitational fluctuations formed in the immediate aftermath of the Big Bang. That has the potential to provide a new view into the earliest history of the Universe, one that’s completely independent of the cosmic microwave background.

Now that I have you all as excited as I am, I regret to inform you that the launch date isn’t planned until 2034. So, hang in there for a decade—I promise it will be worth it.

LIGO goes to space: ESA to proceed with LISA gravitational wave detector Read More »

explaining-why-a-black-hole-produces-light-when-ripping-apart-a-star

Explaining why a black hole produces light when ripping apart a star

astronomy, astrophysics, black holes, Science, tidal disruption / /
Image of a multi-colored curve, with two inset images of actual astronomical objects.

Enlarge / A model of a tidal disruption, along with some observations of one.

Supermassive black holes appear to be present at the core of nearly every galaxy. Every now and again, a star wanders too close to one of these monsters and experiences what’s called a tidal disruption event. The black hole’s gravity rips the star to shreds, resulting in a huge burst of radiation. We’ve observed this happening several times now.

But we don’t entirely know why it happens—”it” specifically referring to the burst of radiation. After all, stars produce radiation through fusion, and the tidal disruption results in the spaghettification of the star, effectively pulling the plug on the fusion reactions. Black holes brighten when they’re feeding on material, but that process doesn’t look like the sudden burst of radiation from a tidal disruption event.

It turns out that we don’t entirely know how the radiation is produced. There are several competing ideas, but we’ve not been able to figure out which one of them fits the data best. However, scientists have taken advantage of an updated software package to model a tidal disruption event and show that their improved model fits our observations pretty well.

Spaghettification simulation

As mentioned above, we’re not entirely sure about the radiation source in tidal disruption events. Yes, they’re big and catastrophic, and so a bit of radiation isn’t much of a surprise. But explaining the details of that radiation—what wavelengths predominate, how quickly its intensity rises and falls, etc.—can tell us something about the physics that dominates these events.

Ideally, software should act as a bridge between the physics of a tidal disruption and our observations of the radiation they produce. If we simulate a realistic disruption and have the physics right, then the software should produce a burst of radiation that is a decent match for our observations of these events. Unfortunately, so far, the software has let us down; to keep things computationally manageable, we’ve had to take a lot of shortcuts that have raised questions about the realism of our simulations.

The new work, done by Elad Steinberg and Nicholas Stone of The Hebrew University, relies on a software package called RICH that can track the motion of fluids (technically called hydrodynamics). And, while a star’s remains aren’t fluid in the sense of the liquids we’re familiar with here on Earth, their behavior is primarily dictated by fluid mechanics. RICH was recently updated to better model radiation emission and absorption by the materials in the fluid, which made it a better fit for modeling tidal disruptions.

The researchers still had to take a few shortcuts to ensure that the computations could be completed in a realistic amount of time. The version of gravity used in the simulation isn’t fully relativistic, and it’s only approximated in the area closest to the black hole. But that sped up computations enough that the researchers could track the remains of the star from spaghettification to the peak of the event’s radiation output, a period of nearly 70 days.

Explaining why a black hole produces light when ripping apart a star Read More »