By combining data from Chandra and several other telescopes, astronomers have identified the true nature of an unusual source in the Milky Way galaxy. This discovery implies that there could be a much larger number of black holes in the Galaxy that have previously been unaccounted for. For about two decades, astronomers have known about an object called VLA J213002.08+120904 (VLA J2130+12 for short). Although it is close to the line of sight to the globular cluster M15, most astronomers had thought that this source of bright radio waves was probably a distant galaxy.

Thanks to recent distance measurements with an international network of radio telescopes, including the EVN (European Very Long Baseline Interferometry Network) telescopes, the NSF's Green Bank Telescope and Arecibo Observatory, astronomers realized that VLA J2130+12 is at a distance of 7,200 light years, showing that it is well within our own Milky Way galaxy and about five times closer than M15. A deep image from Chandra reveals it can only be giving off a very small amount of X-rays, while recent VLA data indicates the source remains bright in radio waves.

This new study indicates that VLA J2130+12 is a black hole a few times the mass of our Sun that is very slowly pulling in material from a companion star. At this paltry feeding rate, VLA J2130+12 was not previously flagged as a black hole since it lacks some of the telltale signs that black holes in binaries typically display.

"Usually, we find black holes when they are pulling in lots of material. Before falling into the black hole this material gets very hot and emits brightly in X-rays," said Bailey Tetarenko of the University of Alberta, Canada, who led the study. "This one is so quiet that it's practically a stealth black hole."

This is the first time a black hole binary system outside of a globular cluster has been initially discovered while it is in such a quiet state.

Hubble observations identified VLA J2130+12 with a star having only about one-tenth to one-fifth the mass of the Sun. The observed radio brightness and the limit on the X-ray brightness from Chandra allowed the researchers to rule out other possible interpretations, such as an ultra-cool dwarf star, a neutron star, or a white dwarf pulling material away from a companion star.

In the graphic below, the images on the left show X-rays from Chandra and an optical image from Hubble of a large area around the source VLA J2130+12, including M15. The images on the right show the source VLA J2130+12 that is bright in radio waves, but can only be giving off a very small amount of X-rays. These pieces of information indicate the source contains a black hole with a few times the mass of the Sun.

Because this study only covered a very small patch of sky, the implication is that there should be many of these quiet black holes around the Milky Way. The estimates are that tens of thousands to millions of these black holes could exist within our Galaxy, about three to thousands of times as many as previous studies have suggested.

"Unless we were incredibly lucky to find one source like this in a small patch of the sky, there must be many more of these black hole binaries in our Galaxy than we used to think," said co-author Arash Bahramian, also of the University of Alberta.

There are other implications of finding that VLA J2130+12 is relatively near to us. "Some of these undiscovered black holes could be closer to the Earth than we previously thought," said Robin Arnason, a co-author from Western University, Canada "However there's no need to worry as even these black holes would still be many light years away from Earth."

Sensitive radio and X-ray surveys covering large regions of the sky will need to be performed to uncover more of this missing population. If, like many others, this black hole was formed in the plane of the Milky Way's disk, it would have needed a large kick at birth to launch it to its current position about 3,000 light years above the plane of the Galaxy.

The Daily Galaxy via International Center for Radio Astronomy Research

Image Credit: X-ray: NASA/CXC/Univ. of Alberta/B.Tetarenko et al; Optical: NASA/STScI; Radio: NSF/AUI/NRAO/Curtin Univ./J. Miller-Jones) and ALMA Observatory

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Astronomers have long known that organic molecules form in diffuse gas clouds floating between stars. It is thought that as the Solar System formed 4.6 billion years ago, some of these organic molecules were transported from interstellar space to the planet forming disk. Later, these molecules played important roles in the chemical evolution resulting in the emergence of life on the Earth.

However, it is still unknown what kinds and quantities of organic molecules were actually supplied from interstellar space. Although radio astronomy observations during the last decade showed that saturated complex organic molecules, such as methanol (CH3OH) and methyl formate (HCOOCH3) [1], exist around Solar-type protostars, their distributions were too compact to be resolved with the radio telescopes available at the time.

With ALMA, an international team lead by Yoko Oya, a graduate student of Department of Physics, The University of Tokyo, and Nami Sakai, an associate chief scientist of RIKEN, studied the distribution of various organic molecules around a Solar-type protostar IRAS 16293-2422A at a high spatial resolution. They discovered a ring structure of complex organic molecules around the protostar. The radius of the ring is 50 times wider than the Earth's orbit. This size is comparable to the size of the Solar System, and the ring structure most likely represents the boundary region between infalling gas and a rotating disk structure around the protostar.

The observations clearly showed the distribution of large organic molecules methyl formate (HCOOCH3) and carbonyl sulfide (OCS). Apparently the distribution of methyl formate is confined in a more compact area around the protostar than the OCS distribution, which mainly traces the infalling gas. "When we measured the motion of the gas containing methyl formate by using the Doppler effect," said Oya "we found a clear rotation motion specific to the ring structure." In this way, they identified the rotating ring structure of methyl formate, although it is not resolved spatially. A similar ring structure is also found for methanol.

These saturated organic molecules are formed in interstellar space and are preserved on the surfaces of dust grains. Around the outer boundary of the disk structure, they evaporate due to shock generated by collisions of the disk and infalling material, and/or due to heating by the light from the baby star. This result is the first direct evidence that interstellar organic materials are indeed fed into the rotating disk structure that eventually forms a planetary system.

In 2014, the team found a similar ring structure of SO (sulfur monoxide) around another Solar-type protostar L1527. In this source, unsaturated complex organic molecules such as CCH and cyclic-C3H2 are very abundant in the infalling gas, while SO preferentially exists in the boundary between the infalling gas and the disk structure. Although the physical structure in L1527 is similar to that found in IRAS 16293-2422A, the chemical composition is much different. Saturated complex organic molecules are almost completely absent in L1527.

The present result, taken together with previous results on L1527, clearly demonstrates for the first time that the materials delivered to a planetary system differ from star to star. A new perspective on chemical composition is thus indispensable for a thorough understanding of the origin of the Solar System and the origin of life on the Earth.

The Daily Galaxy via National Institutes of Natural Sciences

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A Southwest Research Institute-led team has discovered an elusive, dark moon orbiting Makemake, one of the "big four" dwarf planets populating the Kuiper Belt region at the edge of our solar system. The findings are detailed in the paper "Discovery of a Makemakean Moon," published in the June 27 issue of Astrophysical Journal Letters.

"Makemake's moon proves that there are still wild things waiting to be discovered, even in places people have already looked," said Dr. Alex Parker, lead author of the paper and the SwRI astronomer credited with discovering the satellite. Parker spotted a faint point of light close to the dwarf planet using data from Hubble's Wide Field Camera 3. "Makemake's moon -- nicknamed MK2 -- is very dark, 1,300 times fainter than the dwarf planet."

A nearly edge-on orbital configuration helped it evade detection, placing it deep within the glare of the icy dwarf during a substantial fraction of its orbit. Makemake is one of the largest and brightest known Kuiper Belt Objects (KBOs), second only to Pluto. The moon is likely less than 100 miles wide while its parent dwarf planet is about 870 miles across. Discovered in 2005, Makemake is shaped like football and sheathed in frozen methane.

"With a moon, we can calculate Makemake's mass and density," Parker said. "We can contrast the orbits and properties of the parent dwarf and its moon, to understand the origin and history of the system. We can compare Makemake and its moon to other systems, and broaden our understanding of the processes that shaped the evolution of our solar system."

With the discovery of MK2, all four of the currently designated dwarf planets are known to host one or more satellites. The fact that Makemake's satellite went unseen despite previous searches suggests that other large KBOs may host hidden moons.

Prior to this discovery, the lack of a satellite for Makemake suggested that it had escaped a past giant impact. Now, scientists will be looking at its density to determine if it was formed by a giant collision or if it was grabbed by the parent dwarf's gravity. The apparent ubiquity of moons orbiting KBO dwarf planets supports the idea that giant collisions are a near-universal fixture in the histories of these distant worlds.

The Daily Galaxy via Southwest Research Institute

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"The dips found by Kepler are real. Something seems to be transiting in front of this star and we still have no idea what it is!" confirms German astronomer Michael Hippke. Even if aliens are not involved, Tabby's star remains "the most mysterious star in the universe" as Yale astronomer Tabetha Boyajian described it in a TED talk she gave last February.

The results of a new study make it far less likely that KIC 8462852, popularly known as Tabby's star, is the home of industrious aliens who are gradually enclosing it in a vast shell called a Dyson sphere. Media interest went viral last October when a group of astronomers from Pennsylvania State University released a preprint that cited KIC 8462852's "bizarre light curve" as "consistent with" a swarm of alien-constructed megastructures.

Public interest in the star, which sits about 1,480 light-years away in the constellation Cygnus, began last fall("Tabby") Boyajian and colleagues posted a paper on an astronomy preprint server reporting that "planet hunters" - a citizen science group formed to search data from the Kepler space telescope for evidence of exoplanets - had found unusual fluctuations in the light coming from the otherwise ordinary F-type star (slightly larger and hotter than the sun).

The most remarkable of these fluctuations consisted of dozens of uneven, unnatural-looking dips that appeared over a 100-day period indicating that a large number of irregularly shaped objects had passed across the face of the star and temporarily blocked some of the light coming from it.

The top panel of the graphic below shows four years of Kepler observations of the 12th-magnitude star KIC 8462852 in Cygnus. Several sporadic dips in its light output (normalized to 100%) hint that something is partially blocking its light. The portion highlighted in yellow, recorded in February to April 2013, is shown at three different scales along the bottom. The random, irregular shape of each dip could not be caused by a transiting exoplanet. (T. Boyajian & others / MNRAS).

The attention caused scientists at the SETI Institute to train its Alien Telescope Array on the star to see if they could detect any radio signals indicating the presence of an alien civilization. In November it reported finding "no such evidence" of signals with an artificial origin.

Then a study released in January by a Louisiana State University astronomer threw even more fuel on the fire of alien speculation by announcing that the brightness of Tabby's star had dimmed by 20 percent over the last century: a finding particularly difficult to explain by natural means but consistent with the idea that aliens were gradually converting the material in the star's planetary system into giant megastructures that have been absorbing increasing amounts of energy from the star for more than a century. That study has now been accepted for publication in the peer reviewed Astrophysical Journal.

However, a new study - also accepted for publication in the Astrophysical Journal - has taken a detailed look at the observations on which the LSU study was based and concluded there is no credible evidence that the brightness of the star been steadily changing over this period.

When the LSU study was posted on the physics preprint server ArXiv, it caught the attention of Vanderbilt doctoral student Michael Lund because it was based on data from a unique resource: Digital Access to a Sky Century @ Harvard. DASCH consists of more than 500,000 photographic glass plates taken by Harvard astronomers between 1885 and 1993, which the university is digitizing. Lund was concerned that the apparent 100-year dimming of Tabby's star might just be the result of observations having been made by a number of different telescopes and cameras that were used during the past century.

Lund convinced his advisor, Professor of Physics and Astronomy Keivan Stassun, and a frequent collaborator, Lehigh University astronomer Joshua Pepper, that the question was worth pursuing. After they began the study, the Vanderbilt/Lehigh group discovered that another team - German amateur astronomer Michael Hippke and NASA Postdoctoral Fellow Daniel Angerhausen - were conducting research along similar lines. So the two teams decided to collaborate on the analysis, which they wrote up and submitted to the Astrophysical Journal.

"Whenever you are doing archival research that combines information from a number of different sources, there are bound to be data precision limits that you must take into account," said Stassun. "In this case, we looked at variations in the brightness of a number of comparable stars in the DASCH database and found that many of them experienced a similar drop in intensity in the 1960's. That indicates the drops were caused by changes in the instrumentation not by changes in the stars' brightness."

The planet hunters first detected something unusual in the star's light curve in 2009. They found a 1 percent dip that lasted a week. This is comparable to the signal that would be produced by a Jupiter-sized planet passing in front of the star. But planets produce symmetric dips and the one they found was decidedly asymmetric, like something that would be produced by an irregular-shaped object like a comet.

The light from the star remained steady for two years, then it suddenly took a 15 percent plunge that lasted for a week.
Another two years passed without incident but in 2013 the star began flickering with a complex series of uneven, unnatural looking dips that lasted 100 days. During the deepest of these dips, the intensity of the light coming from the star dropped 20 percent. According to Boyajian it would take an object 1,000 times the area of the Earth transiting the distant star to produce such a dramatic effect.

"The Kepler data contains other cases of irregular dips like these, but never in a swarm like this," said Stassun.

Boyajian and her colleagues considered a number of possible explanations, including variations in the star's output, the aftermath of an Earth/Moon type planetary collision, interstellar clumps of dust passing between the star and earth, and some kind of disruption by the star's apparent dwarf companion. However, none of their scenarios could explain all of the observations. Their best explanation was a giant comet that fragmented into a cascade of thousands of smaller comets. (This hypothesis took a hit when the LSU study was announced because it could not explain a century-long dimming.)

The Kepler telescope is no longer collecting data in the Cygnus region, but Hippke reports that the mystery has captured the imagination of amateur astronomers around the world so thousands of them are pointing their telescopes at Tabby's star, snapping images and sending them to the American Association of Variable Star Observers in hopes of detecting further dips that will shed new light on this celestial mystery.

The Daily Galaxy via Vanderbilt University

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Scientists have been trying to puzzle out for decades why the universe seems to weigh more than it should, and so far the answer points to dark matter—an invisible substance that they still don't clearly understand and is thought to exist in clumps throughout the universe. Dark matter, believed by physicists to outweigh all the normal matter in the universe by more than five to one, is by definition invisible. But, scientists at MIT and elsewhere have developed a new tool that could test to see if dark matter is detectable.

However, an exotic particle -a "dark photon"- that resembles a photon, but with mass, has been proposed by some theorists to explain dark matter — whose nature is unknown but whose existence can be inferred from the gravitational attraction it exerts on ordinary matter, such as in the way galaxies rotate and clump together.

“We're looking for a massive photon,” explains MIT physics professor Richard Milner. That may seem like a contradiction in terms: Photons, or particles of light, are known to be massless. If it does exist, that would represent a major discovery, Milner says. “It's totally beyond anything we understand about the physical world. A massive photon would be totally different” from anything allowed by the Standard Model, the bedrock of modern particle physics. "It's a tiny effect,” Milner adds, but “it can have enormous consequences for our theories and our understanding. It would be absolutely groundbreaking in physics.”

The experiment known as DarkLight, developed by MIT physics professor Peter Fisher and Milner in collaboration with researchers at the Jefferson National Accelerator Laboratory in Virginia and others, will look for evidence a massive dark photon with a specific energy postulated in one particular theory about dark matter, Milner says. If the planned experiment detects the A' particle, says Roy Holt, a distinguished fellow in the physics division at Argonne National Laboratory says, “it would signal that dark matter could actually be studied in a laboratory setting.”

Meanwhile, team of physicists at the University of California have uploaded on Arvix (the e-print archive with over 100,000 articles in physics) work done by a team in Hungary in 2015 that might have revealed the existence of this fifth force of nature. The Hungarian team, led by Attila Krasznahorkay, examined the possible existence of dark photons that work with dark matter. The Berkeley team has challenged the findings, suggesting that the new particle found by the Hungarian team was not a dark photon, but possibly a protophobic X boson, which might carry a super-short force which acts over just the width of an atomic nucleus.

To prove the existence of the theorized particle, dubbed A' (“A prime”), the Darklight experiment will use a particle accelerator at the Jefferson Lab that has been tuned to produce a very narrow beam of electrons with a megawatt of power. That's a lot of power, Milner says: “You could not put any material in that path,” he says, without having it obliterated by the beam. For comparison, he explains that a hot oven represents a kilowatt of power. “This is a thousand times that,” he says, concentrated into mere millionths of a meter.

The Jefferson Lab's Free Electron Laser, in Virginia, will bombard an oxygen target with a stream of electrons with one megawatt of power. This will be able to test for these massive photons at a mass-energy of up to 100 MeV. It is hoped that this hugely powerful beam of electrons will hit the target and create this theorized form of dark matter (A' particles). The dark matter, if it's created, will then immediately decay into two other particles that can be easily detected.

The MIT paper confirms that the new facility's beam meets the characteristics needed to definitively detect the hypothetical particle — or rather, to detect the two particles that it decays into, in precise proportions that would reveal its existence. Doing so, however, will require up to two years of further preparations and testing of the equipment, followed by another two years to collect data on millions of electron collisions in the search for a tiny statistical anomaly.

While DarkLight's main purpose is to search for the dark photon A' particle, it also happens to be well suited to addressing other major puzzles in physics, Milner says. It can probe the nature of a reaction, inside stars, in which carbon and helium fuse to form oxygen — a process that accounts for all of the oxygen that now exists in the universe.

“This is the stuff we're all made of,” Milner says, and the rate of this reaction determines how much oxygen exists. While that reaction rate is very hard to measure, Milner says, the DarkLight experiment could illuminate the process in a novel way: “The idea is to do the inverse.” Instead of fusing atoms to form oxygen, the experiment would direct the powerful beam at an oxygen target, causing it to split into carbon and helium. That, Milner says, would provide an indirect way of determining the stellar production rate.

In 2012, Simona Vegetti, a physics fellow at MIT, discovered an entire galaxy made of dark matter just outside the Milky Way. The dark galaxy may host a luminous galaxy made invisible by the dark matter. “The thing people like about dark matter is that it's been able to explain so many observations,” Vegetti said.

Because dark matter reflects no light, the galaxy is elusive. Vegetti worked with an international team of scientists including three from the U.S. and two from the Netherlands. Using the Keck Telescope in Hawaii, they detected the galaxy by studying ripples in the patterns of light rays from the Milky Way, a method known as gravitational lensing.

“It's a dark matter-dominated object,” Vegetti said, “So there might be stars but very little.”

There are thought to be more than 10,000 satellite galaxies attached to our Milky Way galaxy, but only 30 of them are visible, she said. The image above shows the Sagittarius Dwarf Galaxy, named for the constellation in which it is seen from the earth, in the process of colliding and merging with our own Milky Way. “The question becomes are these satellites missing because they don't exist or because they are purely dark? And that's one question we're trying to answer,” she said.

In the image at the top of the page, the bright source in the upper left is an active galaxy in the cluster, Abell 2142, six million light years across that contains hundreds of galaxies and enough gas to make a thousand more. It is one of the most massive objects in the universe.

The Daily Galaxy via MIT, Northwestern, and Physical Review Letters

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