Astronomers discovered nearest dual supermassive black hole
A team of international astronomers using MUSE reported on the first direct dynamical detection of a dual supermassive black hole system (SMBH) in NGC 7727. These supermassive black holes have a separation of only 1,600 light-years (500 parsec), making them the only known pair of supermassive black holes with a sub-kiloparsec separation. Their study recently appeared in Arxiv.
NGC 7727 is a peculiar galaxy located 89 million light-years away in the constellation of Aquarius. It is the product of the merger of two smaller spiral galaxies that took place around one billion years ago. Astronomers suspected that the galaxy hosted two black holes, but they had not been able to confirm their presence until now.
Now, Karina. T. Voggel and colleagues using data from the Multi-Unit Spectroscopic Explorer (MUSE) investigated whether the galaxy hosted two super-massive black holes or not (SMBH).
“It is the first time we find two supermassive black holes that are this close to each other, less than half the separation of the previous record holder,” said lead author Dr. Karina Voggel, an astronomer at the Observatoire astronomique de Strasbourg.
They not only confirmed that nuclei in NGC 7727 host a super-massive black hole but also they measured dynamical black hole mass for the first time.
They found that, SMBH in the photometric center of the galaxy in Nucleus 1 has a mass of 1.54 × 108 M. While, SMBH in the second nucleus, has a mass of 6.33 × 106 M.
“The SMBH in the offset Nucleus 2 makes up 3.0% of its total mass, which means its SMBH is over-massive compared to the MBH − MBulge scaling relation. This confirms it as the surviving nuclear star cluster of a galaxy that has merged with NGC 7727.”
— they added.
This discovery is the first dynamically confirmed dual SMBH system with a projected separation of less than a kiloparsec and the nearest dynamically confirmed dual SMBH at a distance of 27.4 Mpc.
There are likely many more quiescent SMBHs as well as dual SMBH pairs in the local Universe that have been missed by surveys that focus on bright accretion signatures.”
— they concluded.
Featured image: This image, taken with the MUSE instrument on ESO’s Very Large Telescope, shows two bright galactic nuclei, each housing a supermassive black hole, in NGC 7727. Image credit: ESO / Voggel et al.
K.T. Voggel et al. 2021. First direct dynamical detection of a dual super-massive black hole system at sub-kpc separation. A&A, in press; doi: 10.1051/0004-6361/202140827
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Finding plumes at Europa is an exciting prospect, but scientists warn it’ll be tricky, even from up close.
In 2005, images of a brilliant watery plume erupting from the surface of Saturn’s moon Enceladus captivated the world. The giant column of vapor, ice particles, and organic molecules spraying from the moon’s south polar region suggested that there’s a liquid water ocean below Enceladus’ ice shell and confirmed the moon is geologically active. The plume also thrust Enceladus and other worlds in the outer solar system, with no atmospheres and far from the heat of the Sun, toward the top of NASA’s list of places to search for signs of life.
Scientists now are preparing for a mission to another ice-covered ocean world with possible plumes: Jupiter’s moon Europa. Scheduled to launch in 2024, NASA’s Europa Clipper spacecraft will study the moon from its deep interior to its surface to determine whether it has ingredients that make it a viable home for life.
Like Enceladus, Europa is geologically dynamic, meaning both moons generate heat inside as their solid layers stretch and flex from the gravitational tug-of-war with their host planets and neighboring moons. This, instead of heat from the Sun, keeps subsurface water from freezing on these ice-covered moons. The heat may also help produce or circulate life’s chemical building blocks at the seafloors, including carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur.
But that’s where the similarities end.
“A lot of people think Europa is going to be Enceladus 2.0, with plumes constantly spraying from the surface,” said Lynnae Quick, a member of the science team behind Clipper’s Europa Imaging System (EIS) cameras. “But we can’t look at it that way; Europa is a totally different beast,” said Quick, who’s based at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Scientists are drawn to plumes for a couple of reasons. First, they’re undeniably cool: “We’re scientists, but we’re also human,” said Shawn Brooks, who is working with Europa Clipper’s Europa Ultraviolet Spectrograph (Europa-UVS) science team and is based at NASA’s Jet Propulsion Laboratory in Southern California.
But more practically, Brooks said, plumes offer scientists easier access to Europa’s interior. “It all comes down to whether Europa is habitable, and that comes down to having some understanding of what is happening below the surface, which we can’t reach yet,” he said.
In other words, the magic of Europa, an archetype for a potentially habitable world, is hidden from view deep within the moon. Compared to Enceladus, which is the size of Texas, Europa is about a quarter of Earth’s size, or a bit smaller than Earth’s moon. And evidence suggests Europa has a much deeper saltwater ocean than Enceladus, possibly 40 to 100 miles (about 60 to 160 kilometers) deep, which means it could contain about twice as much water as Earth’s oceans. Some scientists hypothesize that Europa’s ocean could be reacting with superheated rocks below its seafloor, possibly through hydrothermal vents. On Earth, such areas are hotbeds of chemical activity that nourishes innumerable creatures.
Scientists say there also could be large pockets of melted water in Europa’s ice shell, which are more likely than the ocean to be the source of plumes. These pockets could produce cozy habitats for organisms as well.
Because it’s much closer to Jupiter than Enceladus is to Saturn, more heat is generated at Europa from friction produced as it circles its host planet. Given that internal heat stimulates geological activity on rocky worlds, Europa is expected to have more extensive geology than Enceladus. Some scientists predict that Europa has plate tectonics that shift and recycle the icy blocks making up the moon’s surface. If so, Europa could be circulating nutrients produced on the surface by radiation from Jupiter, such as oxygen, to pockets of liquid in the ice shell or perhaps to the ocean itself. Through Europa Clipper, scientists will have a chance to test some of their predictions by analyzing the chemical makeup of plumes or the traces they may leave on the surface.
Scientists warn that Europan plumes, even if they’re there, could be hard to detect even from up close. They may be sporadic, and they may be small and thin, given that Europa’s gravity, which is much stronger than Enceladus’, likely would keep these water plumes close to the surface. That’s a drastic departure from Enceladus’ spectacular vapor column: It’s always on and bigger than the moon itself, spraying icy particles hundreds of miles above the surface. “Even if they’re there, Europa’s plumes may not be that photogenic,” Hedman said.
Though Europa Clipper scientists are devising a variety of creative strategies to find active plumes when the spacecraft begins exploring Europa in 2031, they’re not relying on them to understand what’s going on inside the moon. “We don’t have to catch one for a successful mission,” Quick said.
Quick added that every instrument aboard Clipper can contribute evidence of habitable conditions below the surface regardless of active plumes.
A few examples of how the science team will search for potential plumes include Europa Clipper’s camera suite, EIS. It will scout for plumes near Europa’s surface partly by looking for their silhouettes at Europa’s limb, or edge, when the moon is illuminated by the light of Jupiter as it passes in front of the planet. EIS will snap photos of plumes should they appear, as well as plume deposits that might be visible on the surface. The Europa-UVS will also strive to detect plumes in ultraviolet light, including at the edge of the moon when Europa passes in front of nearby stars, and it can measure the chemical makeup of such plumes. A thermal camera, the Europa Thermal Emission Imaging System (E-THEMIS), will look for hotspots on the surface that may be evidence of active or recent eruptions.
The Europa Clipper team is set to succeed whether or not researchers find plumes at Europa, though many scientists hope for a spectacular water show to enrich the mission and our understanding of Europa. “I do suspect Europa is active and letting some material escape,” Hedman said. “But I expect that when we actually get to understand how it’s doing that, it’s not going to be what anyone expected.”
Life as we know it requires liquid water. Astrobiology, a field of science and engineering that describes efforts to find ingredients of life beyond Earth, is a search for planets, dwarf planets, and moons that harbor substantial liquid water. Scientists call these places “ocean worlds.”Credits: NASA’s Goddard Space Flight Center.
More About the Mission
Missions such as Europa Clipper contribute to the field of astrobiology, the interdisciplinary research on the variables and conditions of distant worlds that could harbor life as we know it. While Europa Clipper is not a life-detection mission, it will conduct detailed reconnaissance of Europa and investigate whether the icy moon, with its subsurface ocean, has the capability to support life. Understanding Europa’s habitability will help scientists better understand how life developed on Earth and the potential for finding life beyond our planet.
Managed by Caltech in Pasadena, California, JPL leads the development of the Europa Clipper mission in partnership with the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, for NASA’s Science Mission Directorate in Washington. The Planetary Missions Program Office at NASA’s Marshall Space Flight Center in Huntsville, Alabama, executes program management of the Europa Clipper mission.
Banner image caption: On the left is a view of Europa taken on March 2, 1979, by the Voyager 1 spacecraft. Next is a color image of Europa taken by the Voyager 2 spacecraft during its close encounter on July 9, 1979. On the right is a view of Europa made from images taken by the Galileo spacecraft in the late 1990s. Image credit: NASA/JPL. Download images of Europa here
Using the European Southern Observatory’s Very Large Telescope (ESO’s VLT), astronomers have revealed the closest pair of supermassive black holes to Earth ever observed. The two objects also have a much smaller separation than any other previously spotted pair of supermassive black holes and will eventually merge into one giant black hole.Located in the galaxy NGC 7727 in the constellation Aquarius, the supermassive black hole pair is about 89 million light-years away from Earth. Although this may seem distant, it beats the previous record of 470 million light-years by quite some margin, making the newfound supermassive black hole pair the closest to us yet.
Supermassive black holes lurk at the centre of massive galaxies and when two such galaxies merge, the black holes end up on a collision course. The pair in NGC 7727 beat the record for the smallest separation between two supermassive black holes, as they are observed to be just 1600 light-years apart in the sky. “It is the first time we find two supermassive black holes that are this close to each other, less than half the separation of the previous record holder,” says Karina Voggel, an astronomer at the Strasbourg Observatory in France and lead author of the study published online today in Astronomy & Astrophysics.
“The small separation and velocity of the two black holes indicate that they will merge into one monster black hole, probably within the next 250 million years,” adds co-author Holger Baumgardt, a professor at the University of Queensland, Australia. The merging of black holes like these could explain how the most massive black holes in the Universe come to be.
Voggel and her team were able to determine the masses of the two objects by looking at how the gravitational pull of the black holes influences the motion of the stars around them. The bigger black hole, located right at the core of NGC 7727, was found to have a mass almost 154 million times that of the Sun, while its companion is 6.3 million solar masses.
It is the first time the masses have been measured in this way for a supermassive black hole pair. This feat was made possible thanks to the close proximity of the system to Earth and the detailed observations the team obtained at the Paranal Observatory in Chile using the Multi-Unit Spectroscopic Explorer (MUSE) on ESO’s VLT, an instrument Voggel learnt to work with during her time as a student at ESO. Measuring the masses with MUSE, and using additional data from the NASA/ESA Hubble Space Telescope, allowed the team to confirm that the objects in NGC 7727 were indeed supermassive black holes.
Astronomers suspected that the galaxy hosted the two black holes, but they had not been able to confirm their presence until now since we do not see large amounts of high-energy radiation coming from their immediate surroundings, which would otherwise give them away. “Our finding implies that there might be many more of these relics of galaxy mergers out there and they may contain many hidden massive black holes that still wait to be found,” says Voggel. “It could increase the total number of supermassive black holes known in the local Universe by 30 percent.”
The search for similarly hidden supermassive black hole pairs is expected to make a great leap forward with ESO’s Extremely Large Telescope (ELT), set to start operating later this decade in Chile’s Atacama Desert. “This detection of a supermassive black hole pair is just the beginning,” says co-author Steffen Mieske, an astronomer at ESO in Chile and Head of ESO Paranal Science Operations. “With the HARMONI instrument on the ELT we will be able to make detections like this considerably further than currently possible. ESO’s ELT will be integral to understanding these objects.”
This research was presented in a paper titled “First Direct Dynamical Detection of a Dual Super-Massive Black Hole System at sub-kpc Separation” to appear in Astronomy & Astrophysics (doi: 10.1051/0004-6361/202140827).
The team is composed of Karina T. Voggel (Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg, France), Anil C. Seth (University of Utah, Salt Lake City, USA [UofU]), Holger Baumgardt (School of Mathematics and Physics, University of Queensland, St. Lucia, Australia), Bernd Husemann (Max-Planck-Institut für Astronomie, Heidelberg, Germany [MPIA]), Nadine Neumayer (MPIA), Michael Hilker (European Southern Observatory, Garching bei München, Germany), Renuka Pechetti (Astrophysics Research Institute, Liverpool John Moores University, Liverpool, UK), Steffen Mieske (European Southern Observatory, Santiago de Chile, Chile), Antoine Dumont (UofU), and Iskren Georgiev (MPIA).
The European Southern Observatory (ESO) enables scientists worldwide to discover the secrets of the Universe for the benefit of all. We design, build and operate world-class observatories on the ground — which astronomers use to tackle exciting questions and spread the fascination of astronomy — and promote international collaboration in astronomy. Established as an intergovernmental organisation in 1962, today ESO is supported by 16 Member States (Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), along with the host state of Chile and with Australia as a Strategic Partner. ESO’s headquarters and its visitor centre and planetarium, the ESO Supernova, are located close to Munich in Germany, while the Chilean Atacama Desert, a marvellous place with unique conditions to observe the sky, hosts our telescopes. ESO operates three observing sites: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its Very Large Telescope Interferometer, as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. Also at Paranal ESO will host and operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. Together with international partners, ESO operates APEX and ALMA on Chajnantor, two facilities that observe the skies in the millimetre and submillimetre range. At Cerro Armazones, near Paranal, we are building “the world’s biggest eye on the sky” — ESO’s Extremely Large Telescope. From our offices in Santiago, Chile we support our operations in the country and engage with Chilean partners and society.
NAU PhD candidate Ari Koeppel, as part of a team of scientists from Northern Arizona and Johns Hopkins Universities, recently discovered that water was once present in a unique but brief manner in a region of Mars called Arabia Terra.
Arabia Terra is in the northern latitudes of Mars. Named in 1879 by Italian astronomer Giovanni Schiaparelli, this ancient land covers an area slightly larger than the European continent. Arabia Terra contains craters, volcanic calderas, canyons, and beautiful bands of rock reminiscent of sedimentary rock layers in the Painted Desert or the Badlands.
“We were specifically interested in using rocks on the surface of Mars to get a better understanding of past environments three to four billion years ago and whether there could have been climatic conditions that were suitable for life on the surface,” Koeppel said. “We’re interested in whether there was stable water. How long there could have been stable water. What the atmosphere might have been like. What the temperature on the surface might have been like.”
In order to get a better understanding of what happened to create the rock layers, they focused on thermal inertia. Thermal inertia defines the ability of a material to change temperature. Sand, with small and loose particles, gains and loses heat quickly, while a solid boulder will remain warm long into the evening. By looking at surface temperatures, they were able to determine the physical properties of rocks in their study area. They could tell if a material was loose and eroding away when it otherwise looked like it was solid. “No one had done an in-depth thermal inertia investigation of these really interesting deposits that cover a large portion of the surface of Mars,” said Edwards.
To complete the study, Koeppel used remote-sensing instruments on orbiting satellites. “Just like geologists on Earth, we look at rocks to try to tell stories about past environments,” Koeppel said. “On Mars, we’re a little bit more limited. We can’t just go to a rock outcrop and collect samples—we’re pretty reliant on satellite data. So, there’s a handful of satellites orbiting Mars, and each satellite hosts a collection of instruments. Each instrument plays its own role in helping us describe the rocks that are on the surface.”
Through a series of investigations using this remotely gathered data, they looked at thermal inertia, plus evidence of erosion, the condition of the craters, and what minerals were present.
“We figured out these deposits are much less cohesive than everyone previously thought they were, indicating that this setting could only have had water for only a brief period of time,” said Koeppel. “For some people, that kind of sucks the air out of the story because we often think that having more water for more time means there’s a greater chance of life having been there at one point. But for us, it’s actually really interesting because it brings up a whole set of new questions. What are the conditions that could have allowed there to be water there for a brief amount of time? Could there have been glaciers that melted quickly with outbursts of huge floods? Could there have been a groundwater system that percolated up out of the ground for only a brief period of time only to sink back down?”
Koeppel started in engineering and physics but switched to geological sciences during his master’s program at The City College of New York. He came to NAU to work with Associate Professor Christopher Edwards and immerse himself in the thriving planetary science community of Flagstaff.
“I got into planetary science because of my excitement for exploring worlds beyond Earth. The universe is astoundingly big, even Mars is just the tip of the iceberg,” Koeppel said. “But we’ve been studying Mars for a few decades now, and at this point, we have a huge accumulation of data. We’re beginning to study it at levels that are comparable to ways we’ve been able to study Earth, and it’s a really exciting time for Mars science.”
Caption, top photo: In support of their Mars research, Koeppel (on the left) and Edwards (right) conducted an analog study in a cinder field near Flagstaff, Arizona. At the Flagstaff study site, they were able to collect data in the field and compare it with the data collected from the drones, simulating satellite imagery.
Ari H.D. Koeppel, Christopher S. Edwards, Andrew M. Annex, Kevin W. Lewis, Gabriel J. Carrillo. A fragile record of fleeting water on Mars. Geology, 2021; DOI: 10.1130/G49285.1
While light can’t escape the monstrous gravity of a black hole, that hasn’t kept researchers on a team that includes UO scientists from taking a big step forward in the effort to reveal their secrets.
UO researchers are a key part of LIGO, an international effort to find and understand gravitational waves. Last week, the LIGO team released the largest catalog of gravitational wave data yet, detailing 35 new collisions from their latest data collection run. Fourteen UO researchers, including nine students, contributed to the new release.
“We’re getting better and better,” said Robert Schofield, a research scientist who began working with the UO’s LIGO group in the late 1990s. “This data run is more sensitive than the one before it, and we could see black holes colliding further into space.”
Millions of light years away, violent collisions between black holes and neutron stars send ripples through spacetime. These ripples, called gravitational waves, eventually reach Earth as infinitesimally faint signals. And LIGO’s super-sensitive detectors can pick them up.
Scientists at LIGO, for Laser Interferometer Gravitational-Wave Observatory, spotted the first gravitational waves in 2015, to great excitement that was followed by a Nobel Prize in physics in 2017. Today, thanks to improvements in the technology, detection events are becoming more and more common.
With the LIGO instruments, “we can look at the universe now in a way that other telescopes can’t,” said UO physicist Ray Frey.
“This last observing run included some events that were exceptional on their own, like the first detection of binaries with one neutron star and one black hole,” said UO physicist Ben Farr. “But now, with almost 100 events, what’s just as exciting is the bigger picture that’s coming into focus.”
There’s enough data to start analyzing it in more complex ways, to draw bigger conclusions about the nature of the universe and how black holes are formed.
“It’s important to know what’s out there in the universe, so that when we detect something new, we can compare it to what we know,” said Bruce Edelman, a graduate student in Farr’s lab.
As part of this new data release, Edelman helped lead an analysis of all the black hole and neutron star collisions detected so far.
From a gravitational wave signal, scientists can estimate the masses of the objects that collided and how far they are from Earth. They can also make inferences about what else might have been happening in the vicinity, whether the two merging objects were the only things around, for example, or whether there were other stars nearby that might have been influencing the process. And they can compare those things on a population level, looking for patterns and trends.
The LIGO team has done similar calculations in the past, but there were so few data points that they had to make simplifications that obscured details.
“We’re detecting so many more objects now, so we can get more sophisticated,” Edelman said.
Behind the scenes, there’s another facet to LIGO’s success: A team of scientists dedicated to improving and monitoring LIGO’s instruments, a pair of detectors located in Hanford, Washington, and Livingston, Louisiana. And UO researchers are integral there, too.
Gravitational waves are so faint by the time they reach Earth that they can be drowned out by closer-to-home disturbances most of us wouldn’t even notice. For example, the early LIGO detectors were so sensitive that water going over a dam 30 kilometers away could throw off the data, said Schofield, who co-leads the environmental monitoring at the Hanford detector. He and his colleagues have placed a bevy of sensors around the detectors, which keep track of external disruptions like rumbling traffic or crackling lightning.
Every time there’s a gravitational wave detection, the team must that check that it’s real. Now that the detections are becoming so much more frequent, they’re working to automate the process. Philippe Nguyen, a graduate student in Frey’s lab, is helping lead the push for automation. He wrote and tested computer code that checks the data against other events happening at the same time, to estimate the likelihood that any detected signal is influenced by something happening on Earth.
“We use real-world events to see whether my predictions actually line up what we see with the detector,” Nguyen said, and then adjust the computer program as necessary.
While LIGO is hitting its stride, the team is still working to make it even better. “Right now, I’m working all the time, fixing and improving things so we’ll do better next run,” Schofield said.
The next data collection run is scheduled to begin in December 2022.
“It’s awesome being part of this really motivated group, and it’s awesome seeing so many people so fascinated by it,” said Nguyen. “You really feel like you’re a part of something bigger.”
Featured image: UO scientists are helping fill in gaps in the knowledge of black holes as part of an international team by detecting and analyzing gravity waves from black hole collisions. Credit: LIGO/T. Pyle
The hunt for gravitational waves, ripples in space and time caused by major cosmic cataclysms, could help solve one of the Universe’s other burning mysteries – boson clouds and whether they are a leading contender for dark matter.
Researchers are using powerful instruments, like the advanced Laser Interferometer Gravitational-Wave Observatory (LIGO), advanced Virgo, and KAGRA, that detect gravitational waves up to billions of light years away to locate potential boson clouds.
Boson clouds, made up of ultralight subatomic particles that are almost impossible to detect, have been suggested as a possible source of dark matter – which accounts for about 85 per cent of all matter in the Universe.
Now a major new international study carried out in the LIGO-Virgo-KAGRA collaboration and co-led by researchers from The Australian National University (ANU), offers one of the best leads yet to hunt down these subatomic particles by searching for gravitational waves caused by boson clouds circling black holes.
Dr Lilli Sun, from the ANU Centre for Gravitational Astrophysics, said the study was the first all-sky survey in the world tailored to look for predicted gravitational waves coming from possible boson clouds near rapidly spinning black holes.
“It is almost impossible to detect these ultralight boson particles on Earth,” Dr Sun said.
“The particles, if they exist, have extremely small mass and rarely interact with other matter — which is one of the key properties that dark matter seems to have. Dark matter is material that cannot be seen directly, but we know that dark matter exists because of the effect it has on objects that we can observe.
“But by searching for gravitational waves emitted by these clouds we may be able to track down these elusive boson particles and possibly crack the code of dark matter. Our searches could also allow us to rule out certain ultralight boson particles that our theories say could exist but actually don’t.”
Dr Sun, also an Associate Investigator at the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), said gravitational wave detectors allowed researchers to examine the energy of rapidly rotating black holes extracted by such clouds if they exist.
“We believe these black holes trap a huge number of boson particles in their powerful gravity field, creating a cloud corotating with them. This delicate dance continues for millions of years and keeps generating gravitational waves that hurtle through space,” she said.
While the researchers haven’t yet detected gravitational waves from boson clouds, Dr Sun said gravitational wave science had “opened doors that were previously locked to scientists”.
“Gravitational-wave discoveries not only provide information about mysterious compact objects in the Universe, like black holes and neutron stars, they also allow us to look for new particles and dark matter,” she said.
“Future gravitational wave detectors will certainly open more possibilities. We will be able to reach deeper into the Universe and discover more insights about these particles.
“For example, the discovery of boson clouds using gravitational wave detectors would bring important insights about dark matter and help advance other searches for dark matter. It would also advance our understanding of particle physics more broadly.”
In another significant breakthrough, the study also shed more light on the chance of boson clouds existing in our own galaxy by taking into consideration their ages.
Dr Sun said the strength of any gravitational wave depends on the age of the cloud, with older ones sending out weaker signals.
“The boson cloud shrinks as it loses energy by sending out gravitational waves,” Dr Sun said.
“We learnt that a particular type of boson cloud younger than 1,000 years is not likely to exist anywhere in our galaxy, while clouds that are up to 10 million years old are not likely to exist within about 3,260 light years from Earth.”
Astronomers at The University of Texas at Austin’s McDonald Observatory have discovered an unusually massive black hole at the heart of one of the Milky Way’s dwarf satellite galaxies, called Leo I. Almost as massive as the black hole in our own galaxy, the finding could redefine our understanding of how all galaxies — the building blocks of the universe — evolve. The work is published in a recent issue of The Astrophysical Journal.
The team decided to study Leo I because of its peculiarity. Unlike most dwarf galaxies orbiting the Milky Way, Leo I does not contain much dark matter. Researchers measured Leo I’s dark matter profile — that is, how the density of dark matter changes from the outer edges of the galaxy all the way into its center. They did this by measuring its gravitational pull on the stars: The faster the stars are moving, the more matter there is enclosed in their orbits. In particular, the team wanted to know whether dark matter density increases toward the galaxy’s center. They also wanted to know whether their profile measurement would match previous ones made using older telescope data combined with computer models.
Led by recent UT Austin doctoral graduate María José Bustamante, the team includes UT astronomers Eva Noyola, Karl Gebhardt and Greg Zeimann, as well as colleagues from Germany’s Max Planck Institute for Extraterrestrial Physics (MPE).
For their observations, they used a unique instrument called VIRUS-W on McDonald Observatory’s 2.7-meter Harlan J. Smith Telescope.
When the team fed their improved data and sophisticated models into a supercomputer at UT Austin’s Texas Advanced Computing Center, they got a startling result.
“The models are screaming that you need a black hole at the center; you don’t really need a lot of dark matter,” Gebhardt said. “You have a very small galaxy that is falling into the Milky Way, and its black hole is about as massive as the Milky Way’s. The mass ratio is absolutely huge. The Milky Way is dominant; the Leo I black hole is almost comparable.” The result is unprecedented.
The researchers said the result was different from the past studies of Leo I due to a combination of better data and the supercomputer simulations. The central, dense region of the galaxy was mostly unexplored in previous studies, which concentrated on the velocities of individual stars. The current study showed that for those few velocities that were taken in the past, there was a bias toward low velocities. This, in turn, decreased the inferred amount of matter enclosed within their orbits.
The new data is concentrated in the central region and is unaffected by this bias. The amount of inferred matter enclosed within the stars’ orbits skyrocketed.
The finding could shake up astronomers’ understanding of galaxy evolution, as “there is no explanation for this kind of black hole in dwarf spheroidal galaxies,” Bustamante said.
The result is all the more important as astronomers have used galaxies such as Leo I, called “dwarf spheroidal galaxies,” for 20 years to understand how dark matter is distributed within galaxies, Gebhardt added. This new type of black hole merger also gives gravitational wave observatories a new signal to search for.
“If the mass of Leo I’s black hole is high, that may explain how black holes grow in massive galaxies,” Gebhardt said. That’s because over time, as small galaxies like Leo I fall into larger galaxies, the smaller galaxy’s black hole merges with that of the larger galaxy, increasing its mass.
Built by a team at MPE in Germany, VIRUS-W is the only instrument in the world now that can do this type of dark matter profile study. Noyola pointed out that many southern hemisphere dwarf galaxies are good targets for it, but no southern hemisphere telescope is equipped for it. However, the Giant Magellan Telescope (GMT) now under construction Chile was, in part, designed for this type of work. UT Austin is a founding partner of the GMT.
Featured image: McDonald Observatory astronomers have found that Leo I (inset), a tiny satellite galaxy of the Milky Way (main image), has a black hole nearly as massive as the Milky Way’s. Leo I is 30 times smaller than the Milky Way. The result could signal changes in astronomers’ understanding of galaxy evolution. Credit: ESA/Gaia/DPAC; SDSS (inset) McDonald Observatory astronomers have found that Leo I (inset), a tiny satellite galaxy of the Milky Way (main image), has a black hole nearly as massive as the Milky Way’s. Leo I is 30 times smaller than the Milky Way. The result could signal changes in astronomers’ understanding of galaxy evolution. Credit: ESA/Gaia/DPAC; SDSS (inset)
Researchers have predicted the new class of star’s existence for 50 years but until now, never observed it in space.
Researchers at the Center for Astrophysics | Harvard & Smithsonian have observed a new type of binary star that has long been theorized to exist. The discovery finally confirms how a rare type of star in the universe forms and evolves.
The new class of stars, described in this month’s issue of the Monthly Notices of the Royal Astronomical Society, was discovered by postdoctoral fellow Kareem El-Badry using the Shane Telescope at Lick Observatory in California and data from several astronomical surveys.
“We have observed the first physical proof of a new population of transitional binary stars,” says El-Badry. “This is exciting; it’s a missing evolutionary link in binary star formation models that we’ve been looking for.”
A New Type of Star
When a star dies, there’s a 97 percent chance it will become a white dwarf, a small dense object that has contracted and dimmed after burning through all its fuel.
But in rare instances, a star can become an extremely low mass (ELM) white dwarf. Less than one-third the mass of the Sun, these stars present a conundrum: if stellar evolution calculations are correct, all ELM white dwarfs would seem to be more than 13.8 billion years old — older than the age of the universe itself and thus, physically impossible.
Over the years, astronomers have concluded that the only way for an ELM white dwarf to form is with the help of a binary companion. The gravitational pull from a nearby companion star could quickly (at least, in less than 13.8B years) eat away at a star until it became an ELM white dwarf.
But evidence for this picture is not foolproof.
Astronomers have observed normal, massive stars like our Sun accreting onto white dwarfs — something called cataclysmic variables. They have also observed ELM white dwarfs with normal white dwarf companions. They had not, however, observed the transitional phase of evolution, or the transformation in between: when the star has lost most of its mass and has nearly contracted to an ELM white dwarf.
A Missing Evolutionary Link
El-Badry often compares stellar astronomy to 19th century zoology.
“You go out into the jungle and find an organism. You describe how big it is, how much it weighs — and then you go on to some other organism,” he explains. “You see all these different types of objects and need to piece together how they are all connected.”
In 2020, El-Badry decided to go back into the jungle in search of the star that had long alluded scientists: the pre-ELM white dwarf (also referred to as an evolved cataclysmic variable).
Using new data from Gaia, the space-based observatory launched by the European Space Agency, and the Zwicky Transient Facility at Caltech, El-Badry narrowed down one billion stars to 50 potential candidates.
The astronomer emphasizes the importance of public data from astronomical surveys for his work. “If it weren’t for projects like the Zwicky Transient Facility and Gaia, which represent huge amount of work behind the scenes from hundreds of people — this work just wouldn’t be possible,” he says.
El-Badry then followed-up with close observations of 21 of the stars.
The selection strategy worked. “100 percent of the candidates were these pre-ELMs we’d been looking for,” he says. “They were more puffed up and bloated than ELMs. They also were egg-shaped because the gravitational pull of the other star distorts their spherical shape.”
“We found the evolutionary link between two classes of binary stars — cataclysmic variables and ELM white dwarfs — and we found a decent number of them,” El-Badry adds.
Thirteen of the stars showed signs that they were still losing mass to their companion, while eight of the stars seemed to no longer be losing mass. Each of them was also hotter in temperature than previously observed cataclysmic variables.
El-Badry plans to continue studying the pre-ELM white dwarfs and may follow-up on the 29 other candidate stars he previously discovered.
Like modern-day anthropologists who are filling the gaps in human evolution, he is amazed by the rich diversity of stars that can arise from simple science.
Featured image: M.Weiss/Center for Astrophysics | Harvard & Smithsonian
A new study, based on the analysis of cone fractures found at the Impact Structure in Santa Fe, presents a method for finding meteorite impact sites, even in the absence of craters. The key is the reduced level of natural magnetization of the rocks. The discovery could favor the study not only of terrestrial geology but also of other bodies in the solar system. All the details on Scientific Reports
A study published in Scientific Reports presented a new method for finding and characterizing meteorite impact sites, even in the absence of characteristic craters. The key would be the greatly reduced level of natural magnetization of the rocks, subjected to the intense forces generated by a meteor as it approaches and hits the surface.
In 2005, along an old road that intersects with Road 475 in New Mexico, in the United States, between Santa Fe and Hyde Memorial State Park , a geologist noticed very peculiar rocks called wedge fractures ( shatter cones , in English). They are truly “unique” structures as they are believed to form when a rock is subjected to a high-pressure, high-speed shock wave, as in the – fortunately unlikely – case of a meteorite or a nuclear explosion.
Normally, rocks not altered by artificial forces or of non-terrestrial origin, have a natural magnetization ranging from 2 to 3 percent, i.e. they are made up of that percentage of magnetic grains (usually magnetite, hematite, or both). Gunther Kletetschka of the University of Alaska Fairbanks , first author of the study, found that the samples collected at the Impact Structure in Santa Fe – which originated about 1.2 billion years ago – are characterized by a much lower magnetization, less than 0.1 per one hundred . According to Kletetschka, the reasons for such low magnetism may lie in the plasma created at the moment of impact and in the change in the behavior of electrons in the atoms of rocks.
Kletetschka’s work will help define an impact site even before wedge fractures are detected, as well as better define the extent of known impact sites that have lost their craters due to erosion. “When an impact occurs, the speed involved is tremendous,” explains Kletetschka. “As soon as there is contact at that speed, there is a change in the kinetic energy into heat, vapor and plasma. Many people expect there to be heat, maybe some melting and evaporation, but they don’t think about plasma. We were able to detect that plasma was created in the rocks during the impact ».
The lines of the Earth’s magnetic field cross the entire planet. Magnetic stability in rocks can be temporarily impaired by a shock wave, such as when hitting an object with a hammer, for example. But after the shock wave passes, it returns as before. In Santa Fe, the impact of the meteorite must have generated a huge shock wave through the rocks, which altered the characteristics of the atoms of the rocks themselves, changing the orbits of some electrons and leading to the loss of magnetism. Furthermore, Kletetschka believes that the impact of the meteorite must have weakened the local magnetic field, which was no longer restored due to the presence of plasma in the rocks. Plasma increased electrical conductivity,superparamagnetic shortly after shock exposure, leaving them magnetized in random orientations and consequently lowering the overall magnetic intensity significantly.
The study not only clarifies how this process was possible, but proposes a new line of research to study impact sites, using the reduction of paleointensity as a new tracer of meteoric impacts.
Featured image: Geologists inspect an outcrop near the sample collection site in New Mexico. Credits: Gunther Kletetschka