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New Evidence of How and When the Milky Way Came Together

Spiral galaxy illustration.
Credit: © AlexMit / 123RF.com

By Jeff Grabmeier | Science Daily

New research provides the best evidence to date into the timing of how our early Milky Way came together, including the merger with a key satellite galaxy.

Using relatively new methods in astronomy, the researchers were able to identify the most precise ages currently possible for a sample of about a hundred red giant stars in the galaxy.

With this and other data, the researchers were able to show what was happening when the Milky Way merged with an orbiting satellite galaxy, known as Gaia-Enceladus, about 10 billion years ago.

Their results were published today (May 17, 2021) in the journal Nature Astronomy.

“Our evidence suggests that when the merger occurred, the Milky Way had already formed a large population of its own stars,” said Fiorenzo Vincenzo, co-author of the study and a fellow in The Ohio State University’s Center for Cosmology and Astroparticle Physics.

Many of those “homemade” stars ended up in the thick disc in the middle of the galaxy, while most that were captured from Gaia-Enceladus are in the outer halo of the galaxy.

“The merging event with Gaia-Enceladus is thought to be one of the most important in the Milky Way’s history, shaping how we observe it today,” said Josefina Montalban, with the School of Physics and Astronomy at the University of Birmingham in the U.K., who led the project.

By calculating the age of the stars, the researchers were able to determine, for the first time, that the stars captured from Gaia-Enceladus have similar or slightly younger ages compared to the majority of stars that were born inside the Milky Way.

A violent merger between two galaxies can’t help but shake things up, Vincenzo said. Results showed that the merger changed the orbits of the stars already in the galaxy, making them more eccentric.

Vincenzo compared the stars’ movements to a dance, where the stars from the former Gaia-Enceladus move differently than those born within the Milky Way. The stars even “dress” differently, Vincenzo said, with stars from outside showing different chemical compositions from those born inside the Milky Way.

The researchers used several different approaches and data sources to conduct their study.

The researchers were able to get such precise ages of the stars through the use of asteroseismology, a relatively new field that probes the internal structure of stars.

Asteroseismologists study oscillations in stars, which are sound waves that ripple through their interiors, said Mathieu Vrard, a postdoctoral research associate in Ohio State’s Department of Astronomy.

“That allows us to get very precise ages for the stars, which are important in determining the chronology of when events happened in the early Milky Way,” Vrard said.

The study also used a spectroscopic survey, called APOGEE, which provides the chemical composition of stars — another aid in determining their ages.

“We have shown the great potential of asteroseismology, in combination with spectroscopy, to age-date individual stars,” Montalban said.

This study is just the first step, according to the researchers.

“We now intend to apply this approach to larger samples of stars, and to include even more subtle features of the frequency spectra,” Vincenzo said.

“This will eventually lead to a much sharper view of the Milky Way’s assembly history and evolution, creating a timeline of how our galaxy developed.”

The work is the result of the collaborative Asterochronometry project, funded by the European Research Council.


Story Source:

Materials provided by Ohio State University. Originally written by Jeff Grabmeier.


Journal Reference:

  1. Josefina Montalbán, J. Ted Mackereth, Andrea Miglio, Fiorenzo Vincenzo, Cristina Chiappini, Gael Buldgen, Benoît Mosser, Arlette Noels, Richard Scuflaire, Mathieu Vrard, Emma Willett, Guy R. Davies, Oliver J. Hall, Martin Bo Nielsen, Saniya Khan, Ben M. Rendle, Walter E. van Rossem, Jason W. Ferguson, William J. Chaplin. Chronologically dating the early assembly of the Milky WayNature Astronomy, 2021; DOI: 10.1038/s41550-021-01347-7



Astronomers Release New All-Sky Map of Milky Way’s Outer Reaches

By NASA/Jet Propulsion Laboratory | Science Daily

Astronomers using data from NASA and ESA (European Space Agency) telescopes have released a new all-sky map of the outermost region of our galaxy. [Editor’s note: See Related Multimedia link below.] Known as the galactic halo, this area lies outside the swirling spiral arms that form the Milky Way’s recognizable central disk and is sparsely populated with stars. Though the halo may appear mostly empty, it is also predicted to contain a massive reservoir of dark matter, a mysterious and invisible substance thought to make up the bulk of all the mass in the universe.

The data for the new map comes from ESA’s Gaia mission and NASA’s Near-Earth Object Wide-Field Infrared Survey Explorer, or NEOWISE, which operated from 2009 to 2013 under the moniker WISE. The study makes use of data collected by the spacecraft between 2009 and 2018.

The new map reveals how a small galaxy called the Large Magellanic Cloud (LMC) — so named because it is the larger of two dwarf galaxies orbiting the Milky Way — has sailed through the Milky Way’s galactic halo like a ship through water, its gravity creating a wake in the stars behind it. The LMC is located about 160,000 light-years from Earth and is less than one-quarter the mass of the Milky Way.

Though the inner portions of the halo have been mapped with a high level of accuracy, this is the first map to provide a similar picture of the halo’s outer regions, where the wake is found — about 200,000 light-years to 325,000 light-years from the galactic center. Previous studies have hinted at the wake’s existence, but the all-sky map confirms its presence and offers a detailed view of its shape, size, and location.

This disturbance in the halo also provides astronomers with an opportunity to study something they can’t observe directly: dark matter. While it doesn’t emit, reflect, or absorb light, the gravitational influence of dark matter has been observed across the universe. It is thought to create a scaffolding on which galaxies are built, such that without it, galaxies would fly apart as they spin. Dark matter is estimated to be five times more common in the universe than all the matter that emits and/or interacts with light, from stars to planets to gas clouds.

Although there are multiple theories about the nature of dark matter, all of them indicate that it should be present in the Milky Way’s halo. If that’s the case, then as the LMC sails through this region, it should leave a wake in the dark matter as well. The wake observed in the new star map is thought to be the outline of this dark matter wake; the stars are like leaves on the surface of this invisible ocean, their position shifting with the dark matter.

The interaction between the dark matter and the Large Magellanic Cloud has big implications for our galaxy. As the LMC orbits the Milky Way, the dark matter’s gravity drags on the LMC and slows it down. This will cause the dwarf galaxy’s orbit to get smaller and smaller until the galaxy finally collides with the Milky Way in about 2 billion years. These types of mergers might be a key driver in the growth of massive galaxies across the universe. In fact, astronomers think the Milky Way merged with another small galaxy about 10 billion years ago.

“This robbing of a smaller galaxy’s energy is not only why the LMC is merging with the Milky Way, but also why all galaxy mergers happen,” said Rohan Naidu, a doctoral student in astronomy at Harvard University and a co-author of the new paper. “The wake in our map is a really neat confirmation that our basic picture for how galaxies merge is on point!”

A Rare Opportunity

The authors of the paper also think the new map — along with additional data and theoretical analyses — may provide a test for different theories about the nature of dark matter, such as whether it consists of particles, like regular matter, and what the properties of those particles are.

“You can imagine that the wake behind a boat will be different if the boat is sailing through water or through honey,” said Charlie Conroy, a professor at Harvard University and an astronomer at the Center for Astrophysics | Harvard & Smithsonian, who co-authored the study. “In this case, the properties of the wake are determined by which dark matter theory we apply.”

Conroy led the team that mapped the positions of over 1,300 stars in the halo. The challenge arose in trying to measure the exact distance from Earth to a large portion of those stars: It’s often impossible to figure out whether a star is faint and closes by or bright and far away. The team used data from ESA’s Gaia mission, which provides the location of many stars in the sky but cannot measure distances to the stars in the Milky Way’s outer regions.

After identifying stars most likely located in the halo (because they were not obviously inside our galaxy or the LMC), the team looked for stars belonging to a class of giant stars with a specific light “signature” detectable by NEOWISE. Knowing the basic properties of the selected stars enabled the team to figure out their distance from Earth and create a new map. It charts a region starting about 200,000 light-years from the Milky Way’s center, or about where the LMC’s wake was predicted to begin and extends about 125,000 light-years beyond that.

Conroy and his colleagues were inspired to hunt for LMC’s wake after learning about a team of astrophysicists at the University of Arizona in Tucson that makes computer models predicting what dark matter in the galactic halo should look like. The two groups worked together on the new study.

One model by the Arizona team, included in the new study, predicted the general structure and specific location of the star wake revealed in the new map. Once the data had confirmed that the model was correct, the team could confirm what other investigations have also hinted at: that the LMC is likely on its first orbit around the Milky Way. If the smaller galaxy had already made multiple orbits, the shape and location of the wake would be significantly different from what has been observed. Astronomers think the LMC formed in the same environment as the Milky Way and another nearby galaxy, M31, and that it is close to completing a long first orbit around our galaxy (about 13 billion years). Its next orbit will be much shorter due to its interaction with the Milky Way.

“Confirming our theoretical prediction with observational data tells us that our understanding of the interaction between these two galaxies, including the dark matter, is on the right track,” said University of Arizona doctoral student in astronomy Nicolás Garavito-Camargo, who led work on the model used in the paper.

The new map also provides astronomers with a rare opportunity to test the properties of the dark matter (the notional water or honey) in our own galaxy. In the new study, Garavito-Camargo and colleagues used a popular dark matter theory called cold dark matter that fits the observed star map relatively well. Now the University of Arizona team is running simulations that use different dark matter theories to see which one best matches the wake observed in the stars.

“It’s a really special set of circumstances that came together to create this scenario that lets us test our dark matter theories,” said Gurtina Besla, a co-author of the study and an associate professor at the University of Arizona. “But we can only realize that test with the combination of this new map and the dark matter simulations that we built.”

Launched in 2009, the WISE spacecraft was placed into hibernation in 2011 after completing its primary mission. In September 2013, NASA reactivated the spacecraft with the primary goal of scanning for near-Earth objects, or NEOs, and the mission and spacecraft were renamed NEOWISE. NASA’s Jet Propulsion Laboratory in Southern California managed and operated WISE for NASA’s Science Mission Directorate. The mission was selected competitively under NASA’s Explorers Program managed by the agency’s Goddard Space Flight Center in Greenbelt, Maryland. NEOWISE is a project of JPL, a division of Caltech, and the University of Arizona, supported by NASA’s Planetary Defense Coordination Office.


Story Source:

Materials provided by NASA/Jet Propulsion LaboratoryNote: Content may be edited for style and length.


Journal Reference:

  1. Charlie Conroy, Rohan P. Naidu, Nicolás Garavito-Camargo, Gurtina Besla, Dennis Zaritsky, Ana Bonaca, Benjamin D. Johnson. All-sky dynamical response of the Galactic halo to the Large Magellanic CloudNature, 2021; 592 (7855): 534 DOI: 10.1038/s41586-021-03385-7



ESO Telescope Spots Galaxies Trapped In The Web of a Supermassive Black Hole

Source: ESO | ScienceDaily

With the help of ESO’s Very Large Telescope (VLT), astronomers have found six galaxies lying around a supermassive black hole when the Universe was less than a billion years old. This is the first time such a close grouping has been seen so soon after the Big Bang and the finding helps us better understand how supermassive black holes, one of which exists at the center of our Milky Way, formed and grew to their enormous sizes so quickly. It supports the theory that black holes can grow rapidly within large, web-like structures that contain plenty of gas to fuel them.

“This research was mainly driven by the desire to understand some of the most challenging astronomical objects — supermassive black holes in the early Universe. These are extreme systems and to date, we have had no good explanation for their existence,” said Marco Mignoli, an astronomer at the National Institute for Astrophysics (INAF) in Bologna, Italy, and lead author of the new research published today in Astronomy & Astrophysics.

The new observations with ESO’s VLT revealed several galaxies surrounding a supermassive black hole, all lying in a cosmic “spider’s web” of gas extending to over 300 times the size of the Milky Way. “The cosmic web filaments are like spider’s web threads,” explains Mignoli. “The galaxies stand and grow where the filaments cross, and streams of gas — available to fuel both the galaxies and the central supermassive black hole — can flow along the filaments.”

The light from this large web-like structure, with its black hole of one billion solar masses, has traveled to us from a time when the Universe was only 0.9 billion years old. “Our work has placed an important piece in the largely incomplete puzzle that is the formation and growth of such extreme, yet relatively abundant, objects so quickly after the Big Bang,” says co-author Roberto Gilli, also an astronomer at INAF in Bologna, referring to supermassive black holes.

The very first black holes, thought to have formed from the collapse of the first stars, must have grown very fast to reach masses of a billion suns within the first 0.9 billion years of the Universe’s life. But astronomers have struggled to explain how sufficiently large amounts of “black hole fuel” could have been available to enable these objects to grow to such enormous sizes in such a short time. The new-found structure offers a likely explanation: the “spider’s web” and the galaxies within it contain enough gas to provide the fuel that the central black hole needs to quickly become a supermassive giant.

But how did such large web-like structures form in the first place? Astronomers think giant halos of mysterious dark matter are key. These large regions of invisible matter are thought to attract huge amounts of gas in the early Universe; together, the gas and the invisible dark matter form the web-like structures where galaxies and black holes can evolve.

“Our finding lends support to the idea that the most distant and massive black holes form and grow within massive dark matter halos in large-scale structures, and that the absence of earlier detections of such structures was likely due to observational limitations,” says Colin Norman of Johns Hopkins University in Baltimore, US, also a co-author on the study.

The galaxies now detected are some of the faintest that current telescopes can observe. This discovery required observations over several hours using the largest optical telescopes available, including ESO’s VLT. Using the MUSE and FORS2 instruments on the VLT at ESO’s Paranal Observatory in the Chilean Atacama Desert, the team confirmed the link between four of the six galaxies and the black hole. “We believe we have just seen the tip of the iceberg, and that the few galaxies discovered so far around this supermassive black hole are only the brightest ones,” said co-author Barbara Balmaverde, an astronomer at INAF in Torino, Italy.

These results contribute to our understanding of how supermassive black holes and large cosmic structures formed and evolved. ESO’s Extremely Large Telescope, currently under construction in Chile, will be able to build on this research by observing many fainter galaxies around massive black holes in the early Universe using its powerful instruments.

More information

This research was presented in the paper “Web of the giant: Spectroscopic confirmation of a large-scale structure around the z = 6.31 quasar SDSS J1030+0524” to appear in Astronomy & Astrophysics.

The team is composed of M. Mignoli (INAF, Bologna, Italy), R. Gilli (INAF, Bologna, Italy), R. Decarli (INAF, Bologna, Italy), E. Vanzella (INAF, Bologna, Italy), B. Balmaverde (INAF, Pino Torinese, Italy), N. Cappelluti (Department of Physics, University of Miami, Florida, USA), L. Cassarà (INAF, Milano, Italy), A. Comastri (INAF, Bologna, Italy), F. Cusano (INAF, Bologna, Italy), K. Iwasawa (ICCUB, Universitat de Barcelona & ICREA, Barcelona, Spain), S. Marchesi (INAF, Bologna, Italy), I. Prandoni (INAF, Istituto di Radioastronomia, Bologna, Italy), C. Vignali (Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, Italy & INAF, Bologna, Italy), F. Vito (Scuola Normale Superiore, Pisa, Italy), G. Zamorani (INAF, Bologna, Italy), M. Chiaberge (Space Telescope Science Institute, Maryland, USA), C. Norman (Space Telescope Science Institute & Johns Hopkins University, Maryland, USA).


Story Source:

Materials provided by ESONote: Content may be edited for style and length.


Journal Reference:

  1. Marco Mignoli, Roberto Gilli, Roberto Decarli, Eros Vanzella, Barbara Balmaverde, Nico Cappelluti, Letizia P. Cassarà, Andrea Comastri, Felice Cusano, Kazushi Iwasawa, Stefano Marchesi, Isabella Prandoni, Cristian Vignali, Fabio Vito, Giovanni Zamorani, Marco Chiaberge, Colin Norman. Web of the giant: Spectroscopic confirmation of a large-scale structure around the z = 6.31 quasar SDSS J1030+0524Astronomy & Astrophysics, 2020; 642: L1 DOI: 10.1051/0004-6361/202039045



Researchers Estimate There Are 36 Advanced Alien Civilizations in the Milky Way Galaxy

Nathan Anderson/Unsplash

By Jake Anderson | Creative Commons | TheMindUnleashed.com

(TMU) – Few mysteries rile the imagination like the search for extraterrestrial intelligence. SETI and other groups have spent decades scanning the skies for signals from other worlds and have yet to confirm the existence of ET. While the majority of astrophysicists and astronomers believe there are almost certainly other advanced life forms out there somewhere, the science behind xenology – the study of extraterrestrial life – has been greatly limited by technological constraints.

new study published in The Astrophysical Journal, however, argues that a reasonable estimate can be deduced by using Earth-like planets as a variable in a mathematical equation. The research concludes that there are likely 36 active ET civilizations in the Milky Way galaxy alone.

Astrophysics professor Christopher Conselice, who was chief researcher for the study, says“There should be at least a few dozen active civilizations in our Galaxy under the assumption that it takes 5 billion years for intelligent life to form on other planets, as on Earth.”

First author Tom Westby explains further: “The classic method for estimating the number of intelligent civilizations relies on making guesses of values relating to life, whereby opinions about such matters vary quite substantially. Our new study simplifies these assumptions using new data, giving us a solid estimate of the number of civilizations in our Galaxy.”

Conselice adds“The idea is looking at evolution but on a cosmic scale. We call this calculation the Astrobiological Copernican Limit.”

The classic method Westby refers to is the Drake Equation, which was a 1960s-era probabilistic argument for how to calculate the number of alien species out there.

However, despite the initial optimism, in recent decades the confounding silence from the cosmos has led some to question whether we’re alone. The Fermi Paradox uses its own probabilistic argument to question why, if life is so common in the universe, we haven’t received any messages or seen a single artifact or probe.

Explanations for the Fermi Paradox abound: 1) Alien signals are out there but we can’t decode them 2) Aliens more advanced than us have transcended physical space 3) Alien civilizations die off fairly quickly after gaining intelligence 4) Aliens have quarantined us in a kind of cosmic zoo so that they can study our development.

One of the most logical explanations – that the distance and time that must be overcome to convey a message or spaceship across the incredible gulfs of interstellar space – is touched upon by the new study. The researchers write that the average distance between civilizations is 17,000 light-years.

For context on how massive this distance really is, consider that the nearest star to Earth, Alpha Centauri, is only 4.3 light-years away. With our current fastest speeds, it would take a human probe 78,000 years to reach this star system.

The researchers also say it is exceedingly possible that these civilizations went extinct thousands of years ago.

While visiting even a nearby alien star is out of our reach for the foreseeable future, new technologies in the coming years may allow us to confirm the existence of an alien civilization.

For example, the James Webb Space Telescope, which is scheduled for deployment in the coming year or so, is so powerful it will be able to study the atmospheres of exoplanets and look for “biosignatures.” In other words, we will be able to determine if an advanced species there is using industrial technology that alters the composition of the atmosphere.

The new study also considers how the search for ET reflects on the evolution of our own species:

“Our new research suggests that searches for extraterrestrial intelligent civilizations not only reveals the existence of how life forms, but also gives us clues for how long our own civilization will last. If we find that intelligent life is common then this would reveal that our civilization could exist for much longer than a few hundred years, alternatively if we find that there are no active civilizations in our Galaxy it is a bad sign for our own long-term existence. By searching for extraterrestrial intelligent life — even if we find nothing — we are discovering our own future and fate.”

It’s incredible to ponder the notion of there being over 30 advanced civilizations in our galaxy. Then, when you consider that the Milky Way is just one out of hundreds of billions of galaxies in the observable universe, human comprehension begins to fail.




Planets Far Beyond Our Galaxy Discovered For The First Time By Astrophysicists

Astrophysicists have discovered a group of planets in a galaxy 3.8 billion light-years away.

By Josh Gabbatiss | Independent

Astrophysicists have discovered planets outside our galaxy for the first time ever.

Previously, planets have only been detected within the Milky Way.

However, by measuring an astronomical phenomenon called microlensing, scientists were able to identify a group of distant worlds using data from Nasa’s Chandra X-ray Observatory.

The newly discovered planets ranged from the size of the moon to the size of Jupiter, and their galaxy is 3.8 billion light-years away from our own.

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Scientists Take Viewers on a Virtual Trip to the Center of the Milky Way in this 2-Minute Video

Source: Phys.org

A new visualization provides an exceptional virtual trip—complete with a 360-degree view—to the center of our home galaxy, the Milky Way. This project, made using data from NASA’s Chandra X-ray Observatory and other telescopes, allows viewers to control their own exploration of the fascinating environment of volatile massive stars and powerful gravity around the monster black hole that lies in the center of the Milky Way.

The Earth is located about 26,000 light-years, or about 150,000 trillion miles, from the center of the Galaxy. While humans cannot physically travel there, scientists have been able to study this region by using data from powerful telescopes that can detect light in a variety of forms, including X-ray and infrared light.

This visualization builds on infrared data with the European Southern Observatory’s Very Large Telescope of 30 massive stellar giants called Wolf-Rayet stars that orbit within about 1.5 light years of the center of our Galaxy. Powerful winds of gas streaming from the surface of these stars are carrying some of their outer layers into interstellar space.

When the outflowing gas collides with previously ejected gas from other stars, the collisions produce shock waves, similar to sonic booms, which permeate the area. These shock waves heat the gas to millions of degrees, which causes it to glow in X-rays. Extensive observations with Chandra of the central regions of the Milky Way have provided critical data about the temperature and distribution of this multimillion-degree gas.

Astronomers are interested in better understanding what role these Wolf-Rayet stars play in the cosmic neighborhood at the Milky Way’s center. In particular, they would like to know how the stars interact with the Galactic center’s most dominant resident: the supermassive black hole known as Sagittarius A* (abbreviated Sgr A*). Pre-eminent yet invisible, Sgr A* has the mass equivalent to some four million Suns.

The Galactic Center visualization is a 360-degree movie that immerses the viewer into a simulation of the center of our Galaxy. The viewer is at the location of Sgr A* and is able to see about 25 Wolf-Rayet stars (white, twinkling objects) orbiting Sgr A* as they continuously eject stellar winds (black to red to yellow color scale). These winds collide with each other, and then some of this material (yellow blobs) spirals towards Sgr A*. The movie shows two simulations, each of which starts around 350 years in the past and spans 500 years. The first simulation shows Sgr A* in a calm state, while the second contains a more violent Sgr A* that is expelling its own material, thereby turning off the accretion of clumped material (yellow blobs) that is so prominent in the first portion.

Scientists have used the visualization to examine the effects Sgr A* has on its stellar neighbors. As the strong gravity of Sgr A* pulls clumps of material inwards, tidal forces stretch the clumps as they get closer to the black hole. Sgr A* also impacts its surroundings through occasional outbursts from its vicinity that result in the expulsion of material away from the giant black hole, as shown in the later part of the movie. These outbursts can have the effect of clearing away some of the gas produced by the Wolf-Rayet winds.

Scientists take viewers to the center of the Milky Way
Credit: X-ray: NASA/UMass/D.Wang et al., IR: NASA/STScI

The researchers, led by Christopher Russell of the Pontifical Catholic University of Chile, used the visualization to understand the presence of previously detected X-rays in the shape of a disk that extend about 0.6 light-years outward from Sgr A*. Their work shows that the amount of X-rays generated by these colliding winds depends on the strength of outbursts powered by Sgr A*, and also the amount of time that has elapsed since an eruption occurred. Stronger and more recent outbursts result in weaker X-ray emission.

The information provided by the theoretical modeling and a comparison with the strength of X-ray emission observed with Chandra led Russell and his colleagues to determine that Sgr A* most likely had a relatively powerful outburst that started within the last few centuries. Moreover, their findings suggest the outburst from the  is still affecting the region around Sgr A* even though it ended about one hundred years ago.

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Supermassive Black Hole Devours a Passing Star Creating the Biggest Blast Ever

https://www.youtube.com/watch?v=MEETqJFKEJM

Video Source: Above Science

Last year, the brightest supernova event ever detected was observed. From four billion light years away, a single point in a distant galaxy spontaneously brightened, rose to a peak outshining the entire galaxy, and gradually faded away. At its most luminous, it was twice as bright as any other supernova previously seen, and was 20 times as intrinsically bright as all the stars in the Milky Way combined. Known as ASASSN-15lh, it was first thought to be a supergiant star that went hypernova, over 100 times as bright as a typical supernova. But follow-up observations with Hubble showed this couldn’t be the case at all; the afterglow signals were all wrong in detail. Instead, an even rarer model fits the data best: a spinning black hole devouring a passing star!

Supernovae come in a variety of brightnesses, with the most luminous ones triggered when the core of a massive star collapses. The rapid collapse causes the temperature inside the dying star to skyrocket, resulting in a runaway fusion reaction. Typically, the innermost regions collapse down to a neutron star or a black hole, while the outer layers are expelled close to the speed of light. In the brightest cases of all, the energies inside get so large that photons spontaneously produce pairs of matter and antimatter, lowering the pressure even further and igniting the most intense collapse of all. The runaway reaction that ensues produce copious amounts of new nuclei, enabling the formation of elements all the way up the periodic table, and creating radioactive sources that cause supernova remnants to shine brightly for decades or even centuries after the explosion.

But what this objects showed was different. Supernovae not only emit characteristic signals in terms of brightening, reaching a peak and fading away in the optical, but also display signatures in the X-ray and infrared. This object is too distant for detailed X-ray observations, but was observed in ultraviolet/optical/infrared detail over a 10 month period by the Very Large Telescope, by Hubble, and by ESO’s New Technology Telescope. What they found was a signature that was inconsistent with any known type of supernova. Moreover, even models that represented exotic scenarios couldn’t reproduce the features seen in ASASSN-15lh.

Sometimes, however, a failure to line up with anything seen before can be even more interesting than what would have been the brightest supernova of all time. While supernovae have a gradual rise to a peak and then slowly fall off, this event showed multiple distinct phases, including a puzzling surprise: a rapid re-brightening in the ultraviolet. In addition, the brightest supernovae are always seen to occur in luminous, blue, rapidly star-forming galaxies, since that’s where the most massive stars are created and found. But the galaxy housing ASASSN-15lh is red and of average brightness only; there are no spectacularly large stars inside. In no instances do bright supernovae form in regions like this or exhibit an ultraviolet rebrightening; something else must have been at play.

But all is not lost, as there is a model that fits! Almost every galaxy, even quiet, red ones, contain supermassive black holes at their core. When matter approaches — whether an asteroid, planet, gas cloud or a star — the incredible tidal forces stretch and pinch it, tearing it apart into a long, thin strand. Some of these black holes can rotate incredibly rapidly, causing the matter that falls in to accelerate at different rates depending on the orientation and configuration of the infall, which changes over time. The ASASSN-15lh event not only showed an ultraviolet re-brightening, but a rapid temperature spike at late times as well. If the explanation pans out, this would be the first time we’ve ever observed a rare event of this kind: a massive star disrupted and devoured by an ultramassive, rapidly spinning supermassive black hole.

Classic, non-rotating disruptions as well as all known supernova models have been ruled out as possible explanations, as the light signatures simply fail to match the physical predictions. But quite surprisingly, a rapidly rotating black hole of 100 million solar masses or more could reproduce the observations simply by devouring a relatively low-mass, Sun-like star. As Giorgos Leloudas describes:

We observed the source for 10 months following the event and have concluded that the explanation is unlikely to lie with an extraordinary bright supernova. Our results indicate that the event was probably caused by a rapidly spinning supermassive black hole as it destroyed a low-mass star.
This is no supernova; this is no luminous flare. This is unlike anything we’ve ever seen before, and it’s likely because rapidly rotating supermassive black holes are the exception, rather than the rule.

References: Spinning Black Hole Swallows Star, Surpasses All Supernovae In Brightness




New Research Predicts Billions Of Habitable Planets in the Milky Way Galaxy

Source: Newsy Science

Researchers looking for habitable planets in the Milky Way galaxy are using a model that estimates more planets could support life than previously thought. Their findings indicate the Milky Way is home to billions of planets properly positioned from their parent stars for liquid surface water, and therefore potentially habitable.