The cosmic cow explained - radio signals point to an explosion and a newborn magnetar

Artist's impression of the cosmic cow

Credit: Shanghai Astronomical Observatory, China

Observations using 21 telescopes of the European VLBI Network (EVN) have revealed that a cosmic explosion, called AT2018cow most likely formed a neutron star with an extremely powerful magnetic field - known as a magnetar. The high-resolution radio images produced in this new study show physical properties of the stellar remnant that make alternative explanations less likely, say scientists.

Among short-lived sky phenomena, AT2018cow (The Cow) is an astronomical event like no other. First detected in 2018, it received its memorable name by chance according to alphabetical protocol to classify such events. However, it was not just its name that makes it memorable. AT2018cow was identified in a relatively nearby galaxy (about 200 million light years away). Its proximity, exceptionally brief brightness and unusually high temperature led to widespread attention upon discovery.

Originally discovered with optical telescopes, follow up observations were conducted across wavelengths from X-ray to radio. These observations indicated that there is a ‘central engine' which powered the event. This resulted in theories that the mysterious source could be a supernova - a star whose central core collapsed - or a Tidal Disruption Event (TDE), where a white dwarf star is being ripped apart as it approaches a massive black hole.

In the current study, an international team was led by Prashanth Mohan, astronomer at the Shanghai Astronomical Observatory, China.

"Both these theories suggested that the observed central engine would produce relativistic jets - a high energy expulsion of material. These jets, when aligned with our line of sight, would appear much brighter as ionised matter is accelerated close to the speed of light, and could be responsible for the exceptional brightness of the event. With a network of radio telescopes, we decided to test whether that was the case", explains Tao An.

The team monitored the radio afterglow to search for a relativistic jet from the Cow. They conducted five observations over the course of a year, using a total of 21 telescopes from the European VLBI Network (EVN). The high-resolution radio imaging provided by the EVN, led the team to a surprising conclusion: there was no sign of a relativistic jet.

"These most detailed images in the radio regime do not show any relativistic motion or expansion during this time period. That argues against a jet in the Cow, at least later in its evolution. Instead it seems that the Cow was intrinsically bright and originated from a star exploding as a supernova", says Jun Yang, astronomer at Onsala Space Observatory, Chalmers University of Technology in Sweden.

Further, the astronomers' observations reveal physical conditions that can only be explained by the presence of a neutron star with extremely strong magnetic fields (a magnetar), which was born in the explosion. "We see signs that material from the explosion expanded into a dense, magnetized environment. The way the radio signals faded is just what we might expect if the Cow's "central engine" is a magnetar which formed from the collapse of a star's core" says Prashanth Mohan.

Such characteristics point to another intriguing possibility, the scientists suggest. Interaction of a magnetar with its strongly magnetized environment around it might also produce short enigmatic phenomena known as Fast Radio Bursts (FRBs).

"The EVN is the most sensitive standalone VLBI network in the world that has delivered cutting edge results in the field of transient science. It has by now provided the most accurate localizations of two FRBs. There is an intriguing possibility that there may be a link between FRBs and other type of transient sources (like the event that produced 2018ATcow), but this requires further studies", concludes Zsolt Paragi from the Joint Institute for VLBI ERIC (JIVE).

Source: Joint Institute for VLBI ERIC (JIVE)

---

Publication link

Prashanth Mohan, Tao An, and Jun Yang. The Nearby Luminous Transient AT2018cow: A Magnetar Formed in a Subrelativistically Expanding Nonjetted Explosion. 2020, ApJL, 888, 24 https://iopscience.iop.org/article/10.3847/2041-8213/ab64d1

---

Contact

Assist. Prof. Prashanth Mohan - lead author
Shanghai Astronomical Observatory, China
Email: pmohan@shao.ac.cn

Prof. Tao An - author
Shanghai Astronomical Observatory, China
Email: antao@shao.ac.cn

Dr. Jun Yang - author
Onsala Space Observatory, Sweden
Email: jun.yang@chalmers.se

Zsolt Paragi - EVN contact
The Joint Institute for VLBI ERIC (JIVE), the Netherlands
Email: paragi@jive.eu
Phone: +31 521 596 536

---

Additional information

Observations were conducted with the European Very Long Baseline Interferometry Network (EVN). The EVN is the most sensitive Very Long Baseline Interferometry (VLBI) array in the world, which allows researchers to conduct unique, high-resolution, radio astronomical observations of cosmic radio sources. Data from the EVN is processed at the Joint Institute for VLBI ERIC (JIVE) - an international research infrastructure based in the Netherlands, which also provides support, conducts leading research and forwards technical development in the field of radio astronomy.

A total of 21 antennas from the EVN were involved in these observations: 300 m Arecibo, (USA), 32 m Badary (Russia), 32 m Cambridge (UK), 25 m Defford (UK), 100 m Effelsberg (Germany) 26 m Hartebeesthoek (South Africa), 32 m Irbene (Latvia), 16 m Irbene (Latvia), 76 m Lovell (UK), 40 m Kunming (China), 25 m Knockin (UK), 25 m Medicina (Italy), 25 m Onsala (Sweden), 64 m Sardinia (Italy), 32 m Svetloe (Russia), 65 m Tianma (China), 32 m Torun (Poland), 26 m Urumqi (China), 25 m Westerbork (Netherlands), 40 m Yebes (Spain), 32 m Zelenchukskaya (Russia).

---

Seeing Stars in 3D: The New Horizons Parallax Program

Color images of the Wolf 359 (top) and Proxima Centauri star fields, obtained in late 2019. The large proper motions of both stars (at the center of each image) will cause them to shift by over an arcsecond by April 2020, when NASA's New Horizons spacecraft, nearly five billion miles (8 billion kilometers) from Earth, will image them. A green circle provides a rough estimate of where both stars will appear in the New Horizons images. (Credit: William Keel/University of Alabama/SARA Observatory)

NASA's Pluto-Kuiper Belt mission invites public participation in a record-setting astronomical measurement

Have a good-sized telescope with a digital camera? Then you can team up with NASA's New Horizons mission this spring on a really cool – and record-setting -- deep-space experiment.

In April, New Horizons, which by then will be more than 46 times farther from the Sun than Earth, nearing 5 billion miles (8 billion kilometers) from home, will be used to detect "shifts" in the relative positions of nearby stars as compared with the way they appear to observers on Earth.

The technique is called parallax, and it has been used by astronomers for nearly two centuries to measure the distances of faraway stars; see the accompanying sidebar article for more detail.

On April 22 and 23, New Horizons will take images of two of the very nearest stars, Proxima Centauri and Wolf 359. When combined with Earth-based images made on the same dates, the result will be a record-setting parallax measurement yielding 3D images of these stars popping out of their background star fields that the New Horizons project will share with the public.

The mission team is coordinating the use of astronomical observatories and a public observing campaign to image the same stars on the same day to demonstrate the "parallax" effect.parallax effect

"These exciting 3D images, which we'll release in May, will be as if you had eyes as wide as the solar system and could detect the distance of these stars yourself," said New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute, Boulder, Colorado. "It'll be a truly vivid demonstration of the immense distance New Horizons has traveled, and a cool way to take advantage of the spacecraft's unique vantage point out on the very frontier of our solar system!"

New Horizons' two target stars can be observed by anyone with a camera-equipped, 6-inch or larger telescope. Once New Horizons sends its images to Earth, the mission team will provide them for comparison to images obtained with amateur telescopes. Wolf 359 and Proxima Centauri will appear to shift in position between the Earth-based and space-based images.

In addition, working with New Horizons participating scientist and Queen guitarist Brian May – an astrophysicist himself – the New Horizons team will create and release 3D images showing these two stars.

"For all of history, the fixed stars in the night sky have served as navigation markers," said Tod Lauer, a New Horizons science team member from the National Science Foundation's National Optical-Infrared Astronomy Research Laboratory. "As we voyage out of the solar system and into interstellar space, how the nearer stars shift can serve as a new way to navigate. We will see this for the first time with New Horizons."

Get more details on the New Horizons Parallax program – including background info on the target stars and the best times to take images – at http://pluto.jhuapl.edu/Learn/Get-Involved.php#Parallax-Program.

New Horizons is the first mission to explore Pluto and distant Kuiper Belt. The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, manages the New Horizons mission for NASA's Science Mission Directorate. Alan Stern, of the Southwest Research Institute (SwRI) is the principal investigator and leads the mission; SwRI also leads the science team, payload operations, and encounter science planning, data analyses and archiving. New Horizons is part of the New Frontiers Program managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. APL designed, built and operates the New Horizons spacecraft.

For more information, visit www.nasa.gov/newhorizons and http://pluto.jhuapl.edu.

Source: New Horizon/NASA's Pluto-Kuiper Belt Mission/News

---

What's a Parallax?

The "parallax effect" is when an object appears to shift in position with respect to more distant objects. This is how our sense of depth perception works: each eye has a slightly different perspective, and the brain uses this to figure out which objects are close and which are far away. You can check this by holding up a finger, blinking with each eye, and noting how your finger it jumps back and forth against more distant background objects. You also see a parallax when you rock from side to side to see around someone blocking your view of a more distant object.

In traditional "stellar parallax" measurements, astronomers use Earth's own back-and-forth rocking motion, as it orbits the Sun, to deduce distances to nearby stars. Earth's orbit is about 186 million miles in diameter, so in half a year – the time it takes Earth to go from one side of its orbit to the other – its vantage point to nearby stars will change by that much. The orbit thus serves as a "baseline" for measuring distances. The bigger the baseline, the bigger the parallaxes.

As they wondered how far away the stars were, astronomers in the early 1700s predicted that nearer stars should shift in position more than distant stars as Earth moved around its orbit. Because distances to even the nearest stars are almost a half-million times greater than the baseline provided by Earth's orbit, the effect is subtle. It took until 1838 for Friedrich Bessel to obtain the first parallax observations by observing semi-annual shifts in the position of the star 61 Cygni.

Accurate stellar parallaxes allow us to survey distances to stars throughout our own Milky Way galaxy, and in doing so anchor our ability to measure distances to other galaxies and determine the overall size of the universe itself! The work to obtain ever more precise parallaxes continues today, with data from the European Space Agency's Gaia mission.

As fundamental as stellar parallaxes are to astronomy, however, they are difficult to demonstrate simply because the shifts are typically smaller than the scales on which telescope can easily resolve, so they require exceedingly careful measurement techniques to be accurately detected. An additional complication: all stars have their own random drifts as they orbit around our galaxy, which means that as we wait several months for Earth's movement to provide the parallaxes, the stars are not staying put. The drifts, known as "proper motions," often cause shifts in a star's position larger than its parallax. The solution is to measure the stellar positions over a few years, so that the change in their positions due to Earth's orbit can be recognized and separated from their constant proper motions. This means parallaxes are evident only with careful numerical analysis applied to years of observations.

The great distance of New Horizons from Earth provides a baseline that is 23 times larger than that previously used to measure parallaxes, thus the shifts of the stars seen in comparison of Earth and New Horizons images will be visually obvious. And, because New Horizons and Earth-based observers can image the same fields at the same time, proper motions over time are irrelevant – meaning we can obtain parallaxes instantly!

---

Astronomers Detect Large Amounts of Oxygen in Ancient Star’s Atmosphere

Artistic image of the supernova explosions of the first massive stars that formed in the milky way. the star j0815+4729 was formed from the material ejected by these first supernovae. Credit: Gabriel Pérez Díaz, SMM (IAC)

Maunakea, Hawaii – An international team of astronomers from the University of California San Diego, the Instituto de Astrofísica de Canarias (IAC), and the University of Cambridge have detected large amounts of oxygen in the atmosphere of one of the oldest and most elementally depleted stars known – a “primitive star” scientists call J0815+4729.

This new finding, which was made using W. M. Keck Observatory on Maunakea in Hawaii to analyze the chemical makeup of the ancient star, provides an important clue on how oxygen and other important elements were produced in the first generations of stars in the universe.

The results are published in the January 21, 2020 edition of the The Astrophysical Journal Letters.

“This result is very exciting. It tells us about some of the earliest times in the universe by using stars in our cosmic back yard,” said Keck Observatory Chief Scientist John O’Meara. “I look forward to seeing more measurements like this one so we can better understand the earliest seeding of oxygen and other elements throughout the young universe.”

Oxygen is the third most abundant element in the universe after hydrogen and helium, and is essential for all forms of life on Earth, as the chemical basis of respiration and a building block of carbohydrates. It is also the main elemental component of the Earth’s crust. However, oxygen didn’t exist in the early universe; it is created through nuclear fusion reactions that occur deep inside the most massive stars, those with masses roughly 10 times the mass of the Sun or greater.

Tracing the early production of oxygen and other elements requires studying the oldest stars still in existence. J0815+4729 is one such star; it resides over 5,000 light years away toward the constellation Lynx.

“Stars like J0815+4729 are referred to as halo stars,” explained UC San Diego astrophysicist Adam Burgasser, a co-author of the study. “This is due to their roughly spherical distribution around the Milky Way, as opposed to the more familiar flat disk of younger stars that include the Sun.”

Halo stars like J0815+4729 are truly ancient stars, allowing astronomers a peek into element production early in the history of the universe.

The research team observed J0815+4729 using Keck Observatory’s High-Resolution Echelle Spectrometer (HIRES) on the 10m Keck I telescope. The data, which required more than five hours of staring at the star over a single night, were used to measure the abundances of 16 chemical species in the star’s atmosphere, including oxygen.

“The primitive composition of the star indicates that it was formed during the first hundreds of millions of years after the Big Bang, possibly from the material expelled from the first supernovae of the Milky Way,” said Jonay González Hernández, Ramón y Cajal postdoctoral researcher and lead author of the study.

Keck Observatory’s HIRES data of the star revealed a very unusual chemical composition. While it has relatively large amounts of carbon, nitrogen, and oxygen – approximately 10, 8, and 3 percent of the abundances measured in the Sun – other elements like calcium and iron have abundances around one millionth that of the Sun.

This animation illustrates the earliest epoch of the universe, just after the Big Bang, when the first elements of hydrogen, helium, and lithium were created in the still hot cosmos. These atoms eventually collected to form the first generation of massive stars, which in turn produced heavier elements such as carbon, oxygen, and nitrogen. As these massive stars exploded as supernovae, they released these heavier elements into the universe, eventually collecting on next generation stars such as J0815+4729, with its unusually high abundance of oxygen. Credit: Gabriel Pérez Díaz, SMM (IAC)

“Only a few such stars are known in the halo of our galaxy, but none have such an enormous amount of carbon, nitrogen, and oxygen compared to their iron content,” said David Aguado, a postdoctoral researcher at the University of Cambridge and co-author of the study. 

The search for stars of this type involves dedicated projects that sift through hundreds of thousands of stellar spectra to uncover a few rare sources like J0815+4729, then follow-up observations to measure their chemical composition. 

This star was first identified in data obtained with the Sloan Digital Sky Survey (SDSS), then characterized by the IAC team in 2017 using the Grand Canary Telescope in La Palma, Spain. “Thirty years ago we started at the IAC to study the presence of oxygen in the oldest stars of the Galaxy; those results had already indicated that this element was produced enormously in the first generations of supernovae. However, we could not imagine that we would find a case of enrichment as spectacular as that of this star,” noted Rafael Rebolo, IAC director and co-author of the study.

Source: W. M. Keck Observatory/News

---

About HIRES

The High-Resolution Echelle Spectrometer (HIRES) produces spectra of single objects at very high spectral resolution, yet covering a wide wavelength range. It does this by separating the light into many “stripes” of spectra stacked across a mosaic of three large CCD detectors. HIRES is famous for finding exoplanets. Astronomers also use HIRES to study important astrophysical phenomena like distant galaxies and quasars, and find cosmological clues about the structure of the early universe, just after the Big Bang.

About W. M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two, 10-meter optical/infrared telescopes on the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems.

Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

---

This image from NASA's Spitzer Space Telescope shows the Tarantula Nebula in two wavelengths of infrared light. The red regions indicate the presence of particularly hot gas, while the blue regions are interstellar dust that is similar in composition to ash from coal or wood-burning fires on Earth. Credit: NASA/JPL-Caltech. › Full image and caption

The Tarantula Nebula, seen in this image by the Spitzer Space Telescope, was one of the first targets studied by the infrared observatory after its launch in 2003, and the telescope has revisited it many times since. Now that Spitzer is set to be retired on Jan. 30, 2020, scientists have generated a new view of the nebula from Spitzer data.

This high-resolution image combines data from multiple Spitzer observations, most recently in February and September 2019.

"I think we chose the Tarantula Nebula as one of our first targets because we knew it would demonstrate the breadth of Spitzer's capabilities," said Michael Werner, who has been Spitzer's project scientist since the mission's inception and is based at NASA's Jet Propulsion Laboratory in Pasadena, California. "That region has a lot of interesting dust structures and a lot of star formation happening, and those are both areas where infrared observatories can see a lot of things that you can't see in other wavelengths."

This annotated image from NASA's Spitzer Space Telescope shows the Tarantula Nebula in infrared light. The supernova 1987A and the starburst region R136 are noted. The magenta-colored regions are primarily interstellar dust that is similar in composition to ash from coal or wood fires on Earth. Credit: NASA/JPL-Caltech.  › Full image and caption

Infrared light is invisible to the human eye, but some wavelengths of infrared can pass through clouds of gas and dust where visible light cannot. So scientists use infrared observations to view newborn stars and still-forming "protostars," swaddled in the clouds of gas and dust from which they formed.

Located in the Large Magellanic Cloud - a dwarf galaxy gravitationally bound to our Milky Way galaxy - the Tarantula Nebula is a hotbed of star formation. In the case of the Large Magellanic Cloud, such studies have helped scientists learn about rates of star formation in galaxies other than the Milky Way.

The nebula also hosts R136, a "starburst" region, where massive stars form in extremely close proximity and at a rate far higher than in the rest of the galaxy. Within R136, in an area less than 1 light-year across (about 6 trillion miles, or 9 trillion kilometers), there are more than 40 massive stars, each containing at least 50 times the mass of our Sun. By contrast, there are no stars at all within 1 light-year of our Sun. Similar starburst regions have been found in other galaxies, containing dozens of massive stars - a higher number of massive stars than what is typically found in the rest of their host galaxies. How these starburst regions arise remains a mystery.

On the outskirts of the Tarantula Nebula, you can also find one of astronomy's most-studied stars that has exploded in a supernova. Dubbed 1987A because it was the first supernova spotted in 1987, the exploded star burned with the power of 100 million Suns for months. The shockwave from that event continues to move outward into space, encountering material ejected from the star during its dramatic death.

When the shockwave collides with dust, the dust heats up and begins to radiate in infrared light. In 2006, Spitzer observations saw that light and determined that the dust is largely composed of silicates, a key ingredient in the formation of rocky planets in our solar system. In 2019, scientists used Spitzer to study 1987A to monitor the changing brightness of the expanding shockwave and debris to learn more about how these explosions change their surrounding environment.

More From Spitzer

To see more amazing images from Spitzer, check out the NASA Selfies App, which has a bundle of new Spitzer images. Available for iOS and Android, the app lets you create a snapshot of yourself in a virtual spacesuit, posing in front of gorgeous cosmic locations, including the Tarantula Nebula. Its simple interface lets you snap a photo of yourself, pick your background and share on social media while also providing you some of the science behind the images.

For an even more immersive Spitzer experience, check out the new Spitzer Final Voyage VR experience, which places you in a 360-degree starscape that replicates Spitzer's current location orbiting the Sun, about 160 million miles (260 million kilometers) behind Earth. The narrated video shows you how the infrared telescope operates and what the universe looks like in infrared light. The VR experience is viewable on the Spitzer YouTube channel using mobile-based VR headsets, and in the Exoplanets Excursion VR app via Oculus Rift and HTC Vive headsets.

More information about Spitzer is available at the following site: https://www.nasa.gov/mission_pages/spitzer/main

News Media Contact

Calla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
626-808-2469
calla.e.cofield@jpl.nasa.gov

Source: JPL-Caltech/News

---

For Hottest Planet, a Major Meltdown, Study Shows

Artist's rendering of a "hot Jupiter" called KELT-9b, the hottest known exoplanet - so hot, a new paper finds, that even molecules in its atmosphere are torn to shreds. Credit: NASA/JPL-Caltech › Larger view

Massive gas giants called "hot Jupiters" - planets that orbit too close to their stars to sustain life - are some of the strangest worlds found beyond our solar system. New observations show that the hottest of them all is stranger still, prone to planetwide meltdowns so severe they tear apart the molecules that make up its atmosphere.

Called KELT-9b, the planet is an ultra-hot Jupiter, one of several varieties of exoplanets - planets around other stars - found in our galaxy. It weighs in at nearly three times the mass of our own Jupiter and orbits a star some 670 light-years away. With a surface temperature of 7,800 degrees Fahrenheit (4,300 degrees Celsius) - hotter than some stars - this planet is the hottest found so far.

Now, a team of astronomers using NASA's Spitzer space telescope has found evidence that the heat is too much even for molecules to remain intact. Molecules of hydrogen gas are likely ripped apart on the dayside of KELT-9b, unable to re-form until their disjointed atoms flow around to the planet's nightside.

Though still extremely hot, the nightside's slight cooling is enough to allow hydrogen gas molecules to reform - that is, until they flow back to the dayside, where they're torn apart all over again.

"This kind of planet is so extreme in temperature, it is a bit separate from a lot of other exoplanets," said Megan Mansfield, a graduate student at the University of Chicago and lead author of a new paper revealing these findings. "There are some other hot Jupiters and ultra-hot Jupiters that are not quite as hot but still warm enough that this effect should be taking place."

The findings, published in Astrophysical Journal Letters, showcase the rising sophistication of the technology and analysis needed to probe these very distant worlds. Science is just beginning to peer into the atmospheres of exoplanets, examining the molecular meltdowns of the hottest and brightest.

KELT-9b will stay firmly categorized among the uninhabitable worlds. Astronomers became aware of its extremely hostile environment in 2017, when it was first detected using the Kilodegree Extremely Little Telescope (KELT) system - a combined effort involving observations from two robotic telescopes, one in southern Arizona and one in South Africa.

In the Astrophysical Journal Letters study, the science team used the Spitzer space telescope to parse temperature profiles from this infernal giant. Spitzer, which makes observations in infrared light, can measure subtle variations in heat. Repeated over many hours, these observations allow Spitzer to capture changes in the atmosphere as the planet presents itself in phases while orbiting the star. Different halves of the planet roll into view as it orbits around its star.

That allowed the team to catch a glimpse of the difference between KELT-9b's dayside and its "night." In this case, the planet orbits its star so tightly that a "year" - once around the star - takes only 1 1/2 days. That means the planet is tidally locked, presenting one face to its star for all time (as our Moon presents only one face to Earth). On the far side of KELT-9b, nighttime lasts forever.

But gases and heat flow from one side to the other. A big question for researchers trying to understand exoplanet atmospheres is how radiation and flow balance each other out.

Computer models are major tools in such investigations, showing how these atmospheres are likely to behave in different temperatures. The best fit for the data from KELT-9b was a model that included hydrogen molecules being torn apart and reassembled, a process known as dissociation and recombination.

"If you don't account for hydrogen dissociation, you get really fast winds of [37 miles or] 60 kilometers per second," Mansfield said. "That's probably not likely."

KELT-9b turns out not to have huge temperature differences between its day- and nightsides, suggesting heat flow from one to the other. And the "hot spot" on the dayside, which is supposed to be directly under this planet's star, was shifted away from its expected position. Scientists don't know why - yet another mystery to be solved on this strange, hot planet.

News Media Contact

Calla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
626-808-2469
calla.e.cofield@jpl.nasa.gov

Written by Pat Brennan

Source: JPL-Caltech/News

---

NASA's Kepler Witnesses Vampire Star System Undergoing Super-Outburst

Credits: Artist's Illustration: NASA and L. Hustak (STScI)

NASA's Kepler spacecraft was designed to find exoplanets by looking for stars that dim as a planet crosses the star's face. Fortuitously, the same design makes it ideal for spotting other astronomical transients – objects that brighten or dim over time. A new search of Kepler archival data has uncovered an unusual super-outburst from a previously unknown dwarf nova .

The system brightened by a factor of 1,600 over less than a day before slowly fading away. The star system in question consists of a white dwarf star with a brown dwarf companion about one-tenth as massive as the white dwarf. A white dwarf is the leftover core of an aging Sun-like star and contains about a Sun's worth of material in a globe the size of Earth. A brown dwarf is an object with a mass between 10 and 80 Jupiters that is too small to undergo nuclear fusion. 

The brown dwarf circles the white dwarf star every 83 minutes at a distance of only 250,000 miles (400,000 km) – about the distance from Earth to the Moon. They are so close that the white dwarf's strong gravity strips material from the brown dwarf, sucking its essence away like a vampire. The stripped material forms a disk as it spirals toward the white dwarf (known as an accretion disk).

It was sheer chance that Kepler was looking in the right direction when this system underwent a super-outburst, brightening by more than 1,000 times. In fact, Kepler was the only instrument that could have witnessed it, since the system was too close to the Sun from Earth's point of view at the time. Kepler's rapid cadence of observations, taking data every 30 minutes, was crucial for catching every detail of the outburst.

The event remained hidden in Kepler's archive until identified by a team led by Ryan Ridden-Harper of the Space Telescope Science Institute (STScI), Baltimore, Maryland, and the Australian National University, Canberra, Australia. "In a sense, we discovered this system accidentally. We weren't specifically looking for a super-outburst. We were looking for any sort of transient," said Ridden-Harper.

Kepler captured the entire event, observing a slow rise in brightness followed by a rapid intensification. While the sudden brightening is predicted by theories, the cause of the slow start remains a mystery. Standard theories of accretion disk physics don't predict this phenomenon, which has subsequently been observed in two other dwarf nova super-outbursts.

"These dwarf nova systems have been studied for decades, so spotting something new is pretty tricky," said Ridden-Harper. "We see accretion disks all over – from newly forming stars to supermassive black holes – so it's important to understand them."

Theories suggest that a super-outburst is triggered when the accretion disk reaches a tipping point. As it accumulates material, it grows in size until the outer edge experiences gravitational resonance with the orbiting brown dwarf. This might trigger a thermal instability, causing the disk to get superheated. Indeed, observations show that the disk's temperature rises from about 5,000–10,000° F (2,700–5,300° C) in its normal state to a high of 17,000–21,000° F (9,700–11,700° C) at the peak of the super-outburst.

This type of dwarf nova system is relatively rare, with only about 100 known. An individual system may go for years or decades between outbursts, making it a challenge to catch one in the act.

"The detection of this object raises hopes for detecting even more rare events hidden in Kepler data," said co-author Armin Rest of STScI.

The team plans to continue mining Kepler data, as well as data from another exoplanet hunter, the Transiting Exoplanet Survey Satellite (TESS) mission, in search of other transients.

"The continuous observations by Kepler/K2, and now TESS, of these dynamic stellar systems allows us to study the earliest hours of the outburst, a time domain that is nearly impossible to reach from ground-based observatories," said Peter Garnavich of the University of Notre Dame in Indiana.

This work was published in the Oct. 21, 2019 issue of the Monthly Notices of the Royal Astronomical Society.

The Space Telescope Science Institute is expanding the frontiers of space astronomy by hosting the science operations center of the Hubble Space Telescope, the science and operations center for the James Webb Space Telescope, and the science operations center for the future Wide Field Infrared Survey Telescope (WFIRST). STScI also houses the Mikulski Archive for Space Telescopes (MAST) which is a NASA-funded project to support and provide to the astronomical community a variety of astronomical data archives, and is the data repository for the Hubble, Webb, Kepler, K2, TESS missions and more.

---

Contact:

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland
410-338-4366
cpulliam@stsci.edu

Ryan Ridden-Harper
Space Telescope Science Institute, Baltimore, Maryland, and
Australian National University, Canberra, Australia
rridden@stsci.edu

---

Related Links:

• The science paper by R. Ridden-Harper et al.
• NASA's Kepler Portal
• ANU's Release

---

Supermassive Influence

NGC 1022

Credit: ESA/Hubble & NASA, A. Seth

This peculiar galaxy, beautifully streaked with tendrils of reddish dust, is captured here in wonderful detail by the NASA/ESA Hubble Space Telescope. 

The galaxy is known as NGC 1022, and is officially classified as a barred spiral galaxy. You can just about make out the bar of stars in the centre of the galaxy in this image, with swirling arms emerging from its ends. This bar is much less prominent than in some of the galaxy’s barred cousins and gives the galaxy a rather squat appearance; but the lanes of dust that swirl throughout its disc ensure it is no less beautiful. 

Hubble observed this image as part of a study into one of the Universe’s most notorious residents: black holes. These are fundamental components of galaxies, and are thought to lurk at the hearts of many — if not all — spirals. In fact, they may have quite a large influence over their cosmic homes. Studies suggest that the mass of the black hole sitting at a galaxy’s centre is linked with the larger-scale properties of the galaxy itself. However, in order to learn more, we need observational data of a wider and more diverse range of galaxies — something Hubble’s study aims to provide.

Source: ESA/Hubble/potw

---

Caught “Pink-Handed”

Gum 26

Credit: ESO

The Milky Way contains many regions of starbirth — areas where new stars are springing to life within collapsing clumps of gas and dust. One such region, named Gum 26, is shown here as imaged by the FORS instrument on ESO’s Very Large Telescope in Chile.

Gum 26 is located roughly 20,000 light-years away in the southern constellation of Vela (The Sails). It is something known as an HII region or  emission nebula, where the intense ultraviolet radiation streaming from newly-formed stars ionises the surrounding hydrogen gas, causing it to emit a faint pinkish glow. By catching new stars “pink-handed” in this manner, astronomers can learn more about the conditions under which stars arise, and study how they influence their cosmic environment. 

This image was created as part of the ESO Cosmic Gems programme, an outreach initiative to produce images of interesting, intriguing or visually attractive objects using ESO telescopes, for the purposes of education and public outreach. The programme makes use of telescope time that cannot be used for science observations. All data collected may also be suitable for scientific purposes, and are made available to astronomers through ESO’s science archive.

Source:  ESO/potw

---

Astronomers Discover Class of Strange Objects Near Our Galaxy’s Enormous Black Hole

Artist’s impression of g objects, with the reddish centers, orbiting the supermassive black hole at the center of our galaxy. the black hole is represented as a dark sphere inside a white ring (above the middle of the rendering). Credit: Jack Ciurlo

Maunakea, Hawaii – Astronomers from UCLA and W. M. Keck Observatory have discovered four more bizarre objects at the center of our galaxy, not far from the supermassive black hole called Sagittarius A*, that are now forming a class of their own.

The study, which is part of UCLA’s Galactic Center Orbits Initiative, consists of 13 years of data taken from Keck Observatory on Maunakea in Hawaii; the results published online today in the journal Nature.

“These objects look like gas but behave like stars,” said co-author Andrea Ghez, UCLA’s Lauren B. Leichtman and Arthur E. Levine Professor of Astrophysics and director of the UCLA Galactic Center Group.

This new class of objects, called G objects, look compact most of the time and stretch out when their orbits bring them closest to the black hole. Their orbits range from about 100 to 1,000 years, said lead author Anna Ciurlo, a UCLA postdoctoral researcher.

Ciurlo led the study while participating in Keck Observatory’s Visiting Scholars Program and labeled the four new objects G3, G4, G5 and G6. This set is in addition to the first pair of G objects found near the Galactic Center; G1 was discovered by Ghez’s research group in 2005, followed by G2, which was discovered by astronomers in Germany in 2012.

“The fact that there now several of these objects observed near the  black hole means that they are, most likely, part of a common population,” said co-author Randy Campbell, science operations lead at Keck Observatory.

The researchers have determined orbits for each of the newly discovered G objects. While G1 and G2 have similar orbits, G3, G4, G5, and G6 all have very different orbits.

Ghez and her research team believe that G2 is most likely two stars that had been orbiting the black hole in tandem and merged into an extremely large star, cloaked in unusually thick gas and dust.

“At the time of closest approach, G2 had a really strange signature,” Ghez said. “We had seen it before, but it didn’t look too peculiar until it got close to the black hole and became elongated, and much of its gas was torn apart. It went from being a pretty innocuous object when it was far from the black hole to one that was really stretched out and distorted at its closest approach and lost its outer shell, and now it’s getting more compact again.”

Orbits of the G objects at the center of our galaxy, with the supermassive black hole marked with a white cross. Stars, gas, and dust are in the background. Credit: Anna Ciurlo, Tuan Do/UCLA Galactic Center Group

“One of the things that has gotten everyone excited about the G objects is that the stuff that gets pulled off of them by tidal forces as they sweep by the central black hole must inevitably fall into the black hole,” said co-author Mark Morris, UCLA professor of physics and astronomy. “When that happens, it might be able to produce an impressive fireworks show since the material eaten by the black hole will heat up and emit copious radiation before it disappears across the event horizon.”

Ghez believes all six objects were binary stars — a system of two stars orbiting each other — that merged because of the strong gravitational force of the supermassive black hole. The merging of two stars takes more than 1 million years to complete, Ghez said.

“Mergers of stars may be happening in the universe more often than we thought, and likely are quite common,” Ghez said. “Black holes may be driving binary stars to merge. It’s possible that many of the stars we’ve been watching and not understanding may be the end product of mergers that are calm now. We are learning how galaxies and black holes evolve. The way binary stars interact with each other and with the black hole is very different from how single stars interact with other single stars and with the black hole.”

Ciurlo noted that while the gas from G2’s outer shell got stretched dramatically, its dust inside the gas did not get stretched much. “Something must have kept it compact and enabled it to survive its encounter with the black hole,” Ciurlo said. “This is evidence for a stellar object inside G2.”

“The unique dataset that Professor Ghez’s group has gathered during more than 20 years is what allowed us to make this discovery,” Ciurlo said. “We now have a population of ‘G’ objects, so it is not a matter of explaining a ‘one-time event’ like G2.”

The researchers made the observations using powerful technology that Ghez helped pioneer at Keck Observatory called adaptive optics (AO), which corrects the distorting effects of the Earth’s atmosphere in real time. AO, combined with Keck Observatory’s OH-Suppressing Infrared Imaging Spectrograph (OSIRIS), allowed the team to obtain spectroscopic measurements of the Galactic Center’s gas dynamics.

“The challenge was trying distinguish G objects from a crowded cluster of stars,” said Campbell. “Because their spectra are different from standard stars, we were able to separate them using a tool called the OSIRIS-Volume Display, or OsrsVol.”

The OsrsVol software Campbell developed produces a 3-D spectral data cube that consists of two spatial dimensions plus a wavelength dimension that contains velocity information. This allowed the team to clearly isolate the G-objects and track their movement to see how they behaved around the Milky Way’s supermassive black hole.

In September 2019, Ghez’s team reported that the black hole is getting hungrier and it is unclear why. The stretching of G2 in 2014 appeared to pull off gas that may recently have been swallowed by the black hole, said co-author Tuan Do, a UCLA research scientist and deputy director of the Galactic Center Group.

The research is funded by the National Science Foundation, W. M. Keck Foundation, Keck Visiting Scholars Program, the Gordon and Betty Moore Foundation, the Heising-Simons Foundation, Lauren Leichtman and Arthur Levine, Jim and Lori Keir, and Howard and Astrid Preston.

Source: W.M. Keck Observatory/Science News

---

About Adaptive Optics

W. M. Keck Observatory is a distinguished leader in the field of adaptive optics (AO), a breakthrough technology that removes the distortions caused by the turbulence in the Earth’s atmosphere. Keck Observatory pioneered the astronomical use of both natural guide star (NGS) and laser guide star adaptive optics (LGS AO) and current systems now deliver images three to four times sharper than the Hubble Space Telescope at near-infrared wavelengths. AO has imaged the four massive planets orbiting the star HR8799, measured the mass of the giant black hole at the center of our Milky Way Galaxy, discovered new supernovae in distant galaxies, and identified the specific stars that were their progenitors. Support for this technology was generously provided by the Bob and Renee Parsons Foundation, Change Happens Foundation, Gordon and Betty Moore Foundation, Mt. Cuba Astronomical Foundation, NASA, NSF, and W. M. Keck Foundation.

About OSIRIS

The OH-Suppressing Infrared Imaging Spectrograph (OSIRIS) is one of W. M. Keck Observatory’s “integral field spectrographs.” The instrument works behind the adaptive optics system, and uses an array of lenslets to sample a small rectangular patch of the sky at resolutions approaching the diffraction limit of the 10-meter Keck Telescope. OSIRIS records an infrared spectrum at each point within the patch in a single exposure, greatly enhancing its efficiency and precision when observing small objects such as distant galaxies. It is used to characterize the dynamics and composition of early stages of galaxy formation. Support for this technology was generously provided by the Heising-Simons Foundation and the National Science Foundation.

About W. M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two, 10-meter optical/infrared telescopes on the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems.

Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

---

Astronomers Reveal Interstellar Thread of One of Life’s Building Blocks

PR Image eso2001a

Phosphorus-bearing molecules found in a star-forming region and comet 67P

PR Image eso2001b

ALMA view of the star-forming region AFGL 5142

PR Image eso2001c

Rosetta view of comet 67P/Churyumov–Gerasimenko

PR Image eso2001d

Location of AFGL 5142 in the constellation of Auriga

PR Image eso2001e

Wide-field view of the region of the sky where AFGL 5142 is located

---

Videos 

PR Video 1

ESOcast 215 Light: Interstellar Thread of One of Life’s Building Blocks Revealed

PR Video 2

Zooming into star-forming region AFGL 5142

PR Video 3

Animated view of comet 67P/Churyumov–Gerasimenko

PR Video 4

Animated view of phosphorus-bearing molecules found in a star-forming region and comet 67P

---

ALMA and Rosetta map the journey of phosphorus

Phosphorus, present in our DNA and cell membranes, is an essential element for life as we know it. But how it arrived on the early Earth is something of a mystery. Astronomers have now traced the journey of phosphorus from star-forming regions to comets using the combined powers of ALMA and the European Space Agency’s probe Rosetta. Their research shows, for the first time, where molecules containing phosphorus form, how this element is carried in comets, and how a particular molecule may have played a crucial role in starting life on our planet.

"Life appeared on Earth about 4 billion years ago, but we still do not know the processes that made it possible," says Víctor Rivilla, the lead author of a new study published today in the journal Monthly Notices of the Royal Astronomical Society. The new results from the Atacama Large Millimeter/Submillimeter Array (ALMA), in which the European Southern Observatory (ESO) is a partner, and from the ROSINA instrument on board Rosetta, show that phosphorus monoxide is a key piece in the origin-of-life puzzle.

With the power of ALMA, which allowed a detailed look into the star-forming region AFGL 5142, astronomers could pinpoint where phosphorus-bearing molecules, like phosphorus monoxide, form. New stars and planetary systems arise in cloud-like regions of gas and dust in between stars, making these interstellar clouds the ideal places to start the search for life’s building blocks. 

The ALMA observations showed that phosphorus-bearing molecules are created as massive stars are formed. Flows of gas from young massive stars open up cavities in interstellar clouds. Molecules containing phosphorus form on the cavity walls, through the combined action of shocks and radiation from the infant star. The astronomers have also shown that phosphorus monoxide is the most abundant phosphorus-bearing molecule in the cavity walls.

After searching for this molecule in star-forming regions with ALMA, the European team moved on to a Solar System object: the now-famous comet 67P/Churyumov–Gerasimenko. The idea was to follow the trail of these phosphorus-bearing compounds. If the cavity walls collapse to form a star, particularly a less-massive one like the Sun, phosphorus monoxide can freeze out and get trapped in the icy dust grains that remain around the new star. Even before the star is fully formed, those dust grains come together to form pebbles, rocks and ultimately comets, which become transporters of phosphorus monoxide.

ROSINA, which stands for Rosetta Orbiter Spectrometer for Ion and Neutral Analysis, collected data from 67P for two years as Rosetta orbited the comet. Astronomers had found hints of phosphorus in the ROSINA data before, but they did not know what molecule had carried it there. Kathrin Altwegg, the Principal Investigator for Rosina and an author in the new study, got a clue about what this molecule could be after being approached at a conference by an astronomer studying star-forming regions with ALMA: “She said that phosphorus monoxide would be a very likely candidate, so I went back to our data and there it was!”

This first sighting of phosphorus monoxide on a comet helps astronomers draw a connection between star-forming regions, where the molecule is created, all the way to Earth.

“The combination of the ALMA and ROSINA data has revealed a sort of chemical thread during the whole process of star formation, in which phosphorus monoxide plays the dominant role,” says Rivilla, who is a researcher at the Arcetri Astrophysical Observatory of INAF, Italy’s National Institute for Astrophysics.

“Phosphorus is essential for life as we know it,” adds Altwegg. “As comets most probably delivered large amounts of organic compounds to the Earth, the phosphorus monoxide found in comet 67P may strengthen the link between comets and life on Earth.”

This intriguing journey could be documented because of the collaborative efforts between astronomers. “The detection of phosphorus monoxide was clearly thanks to an interdisciplinary exchange between telescopes on Earth and instruments in space,” says Altwegg.

Leonardo Testi, ESO astronomer and ALMA European Operations Manager, concludes:

“Understanding our cosmic origins, including how common the chemical conditions favourable for the emergence of life are, is a major topic of modern astrophysics. While ESO and ALMA focus on the observations of molecules in distant young planetary systems, the direct exploration of the chemical inventory within our Solar System is made possible by ESA missions, like Rosetta. The synergy between world leading ground-based and space facilities, through the collaboration between ESO and ESA, is a powerful asset for European researchers and enables transformational discoveries like the one reported in this paper.”

---

More Information
This research was presented in a paper to appear in Monthly Notices of the Royal Astronomical Society.

The team is composed of V. M. Rivilla (INAF-Osservatorio Astrofisico di Arcetri, Florence, Italy [INAF-OAA]), M. N. Drozdovskaya (Center for Space and Habitability, University of Bern, Switzerland [CSH]), K. Altwegg (Physikalisches Institut, University of Bern, Switzerland), P. Caselli (Max Planck Institute for Extraterrestrial Physics, Garching, Germany), M. T. Beltrán (INAF-OAA), F. Fontani (INAF-OAA), F.F.S. van der Tak (SRON Netherlands Institute for Space Research, and Kapteyn Astronomical Institute, University of Groningen, The Netherlands), R. Cesaroni (INAF-OAA), A. Vasyunin (Ural Federal University, Ekaterinburg, Russia, and Ventspils University of Applied Sciences, Latvia), M. Rubin (CSH), F. Lique (LOMC-UMR, CNRS–Université du Havre), S. Marinakis (University of East London, and Queen Mary University of London, UK), L. Testi (INAF-OAA, ESO Garching, and Excellence Cluster “Universe”, Germany), and the ROSINA team (H. Balsiger, J. J. Berthelier, J. De Keyser, B. Fiethe, S. A. Fuselier, S. Gasc, T. I. Gombosi, T. Sémon, C. -y. Tzou).

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI). ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It has 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 carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its world-leading 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. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.

Source: ESO/News

---

Links

• Research paper
• Photos of ALMA

---

Contacts

Víctor Rivilla
INAF Arcetri Astrophysical Observatory
Florence, Italy
Tel: +39 055 2752 319
Email: rivilla@arcetri.astro.it

Kathrin Altwegg
University of Bern
Bern, Switzerland
Tel: +41 31 631 44 20
Email: kathrin.altwegg@space.unibe.ch

Leonardo Testi
European Southern Observatory
Garching bei München, Germany
Tel: +49 89 3200 6541
Email: ltesti@eso.org

Bárbara Ferreira
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6670
Cell: +49 151 241 664 00
Email: pio@eso.org

---

Astronomers Find Wandering Massive Black Holes in Dwarf Galaxies

Artist's conception of a dwarf galaxy, its shape distorted, most likely by a past interaction with another galaxy, and a massive black hole in its outskirts (pullout). The black hole is drawing in material that forms a rotating disk and generates jets of material propelled outward. Credit: Sophia Dagnello, NRAO/AUI/NSF. Hi-Res File

Artist's conception of a dwarf galaxy, its shape distorted, most likely by a past interaction with another galaxy, and a massive black hole in its outskirts (bright spot, far right; no pullout). Credit: Sophia Dagnello, NRAO/AUI/NSF. Hi-Res File

Visible-light images of galaxies that VLA observations showed to have massive black holes. Center illustration is artist's conception of the rotating disk of material falling into such a black hole, and the jets of material propelled outward. Credit: Sophia Dagnello, NRAO/AUI/NSF; DECaLS survey; CTIO. Hi-Res File

Roughly half of the newly-discovered black holes are not at the centers of their galaxies

Astronomers seeking to learn about the mechanisms that formed massive black holes in the early history of the Universe have gained important new clues with the discovery of 13 such black holes in dwarf galaxies less than a billion light-years from Earth.

These dwarf galaxies, more than 100 times less massive than our own Milky Way, are among the smallest galaxies known to host massive black holes. The scientists expect that the black holes in these smaller galaxies average about 400,000 times the mass of our Sun.

“We hope that studying them and their galaxies will give us insights into how similar black holes in the early Universe formed and then grew, through galactic mergers over billions of years, producing the supermassive black holes we see in larger galaxies today, with masses of many millions or billions of times that of the Sun,” said Amy Reines of Montana State University.

Reines and her colleagues used the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) to make the discovery, which they are reporting at the American Astronomical Society’s meeting in Honolulu, Hawaii.

Reines and her collaborators used the VLA to discover the first massive black hole in a dwarf starburst galaxy in 2011. That discovery was a surprise to astronomers and spurred a radio search for more.

The scientists started by selecting a sample of galaxies from the NASA-Sloan Atlas, a catalog of galaxies made with visible-light telescopes. They chose galaxies with stars totalling less than 3 billion times the mass of the Sun, about equal to the Large Magellanic Cloud, a small companion of the Milky Way. From this sample, they picked candidates that also appeared in the National Radio Astronomy Observatory’s Faint Images of the Radio Sky at Twenty centimeters (FIRST) survey, made between 1993 and 2011.

They then used the VLA to make new and more sensitive, high-resolution images of 111 of the selected galaxies.

“The new VLA observations revealed that 13 of these galaxies have strong evidence for a massive black hole that is actively consuming surrounding material. We were very surprised to find that, in roughly half of those 13 galaxies, the black hole is not at the center of the galaxy, unlike the case in larger galaxies,” Reines said

The scientists said this indicates that the galaxies likely have merged with others earlier in their history. This is consistent with computer simulations predicting that roughly half of the massive black holes in dwarf galaxies will be found wandering in the outskirts of their galaxies.

“This work has taught us that we must broaden our searches for massive black holes in dwarf galaxies beyond their centers to get a more complete understanding of the population and learn what mechanisms helped form the first massive black holes in the early Universe,” Reines said.

Reines worked with James Condon, of the National Radio Astronomy Observatory; Jeremy Darling, of the University of Colorado, Boulder; and Jenny Greene, of Princeton University. The astronomers are publishing their results in the Astrophysical Journal. (Preprint )

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Media Contact:

Dave Finley, Public Information Officer
(575) 835-7302
dfinley@nrao.edu

Source:  National Radio Astronomy Observatory (NRAO)/News

---

The Turbulent Life of Two Supermassive Black Holes Caught in a Galaxy Crash

NGC 6240 as seen with ALMA (top) and the Hubble Space Telescope (bottom). In the ALMA image, the molecular gas is blue and the black holes are the red dots. The ALMA image provides the sharpest view of the molecular gas around the black holes in this merging galaxy. Credit: ALMA (ESO/NAOJ/NRAO), E. Treister; NRAO/AUI/NSF, S. Dagnello; NASA/ESA Hubble

Artist impression of the merging galaxy NGC 6240

Credit: NRAO/AUI/NSF, S. Dagnello

An international team of astronomers used the Atacama Large Millimeter/submillimeter Array (ALMA) to create the most detailed image yet of the gas surrounding two supermassive black holes in a merging galaxy.

400 million light-years away from Earth, in the constellation of Ophiuchus, two galaxies are crashing into each other and forming a galaxy we know as NGC 6240. This peculiarly-shaped galaxy has been observed many times before, as it is relatively close by. But NGC 6240 is complex and chaotic. The collision between the two galaxies is still ongoing, bringing along in the crash two growing supermassive black holes that will likely merge as one larger black hole.

To understand what is happening within NGC 6240, astronomers want to observe the dust and gas surrounding the black holes in detail, but previous images have not been sharp enough to do that.

New ALMA observations have increased the resolution of the images by a factor of ten – showing for the first time the structure of the cold gas in the galaxy, even within the sphere of influence of the black holes.

“The key to understanding this galaxy system is molecular gas,” explained Ezequiel Treister of the Pontificia Universidad Católica in Santiago, Chile. “This gas is the fuel that is needed to form stars, but it also feeds the supermassive black holes, which allows them to grow.”

Most of the gas is located in a region between the two black holes. Less detailed observations taken previously suggested that this gas might be a rotating disk. “We don’t find any evidence for that,” said Treister. “Instead, we see a chaotic stream of gas with filaments and bubbles between the black holes. Some of this gas is ejected outwards with speeds up to 500 kilometers per second. We don’t know yet what causes these outflows.”

Another reason to observe the gas in such detail is that it helps to determine the mass of the black holes. “Previous models, based on surrounding stars, indicated that the black holes were much more massive than we expected, around a billion times the mass of our Sun,” said Anne Medling of the University of Toledo in Ohio. “But these new ALMA images for the first time showed us how much gas is caught up inside the black holes’ sphere of influence. This mass is significant, and therefore we now estimate the black hole masses to be lower: around a few hundred million times the mass of our Sun. Based on this, we think that most previous black hole measurements in systems like this could be off by 5-90 percent.”

The gas also turned out to be even closer to the black holes than the astronomers had expected. “It is located in a very extreme environment,” explained Medling. “We think that it will eventually fall into the black hole, or it will be ejected at high speeds.”

The astronomers don’t find evidence for a third black hole in the galaxy, which another team recently claimed to have discovered. “We don’t see molecular gas associated with this claimed third nucleus,” said Treister. “It could be a local star cluster instead of a black hole, but we need to study it much more to say anything about it with certainty.”

ALMA’s high sensitivity and resolution are crucial to learn more about supermassive black holes and the role of gas in interacting galaxies. “This galaxy is so complex, that we could never know what is going on inside it without these detailed radio images,” said Loreto Barcos-Muñoz of the National Radio Astronomy Observatory in Charlottesville, Virginia. “We now have a better idea of the 3D-structure of the galaxy, which gives us the opportunity to understand how galaxies evolve during the latest stages of an ongoing merger. In a few hundred million years, this galaxy will look completely different.”

Source: Atacama Large Millimeter/submillimeter Array (ALMA)/Press Release

---

Additional Information

• “The Molecular Gas in the NGC 6240 Merging Galaxy System at the Highest Spatial Resolution,” by E. Treister et al., accepted for publication in The Astrophysical Journal. Preprint.
• “How to Fuel an AGN: Mapping Circumnuclear Gas in NGC 6240 with ALMA,” by A. M. Medling et al., The Astrophysical Journal Letters. https://iopscience.iop.org/article/10.3847/2041-8213/ab4db7

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

---

Contacts

Nicolás Lira
Education and Public Outreach Coordinator
Joint ALMA Observatory, Santiago - Chile
Phone: +56 2 2467 6519
Cell phone: +56 9 9445 7726
Email: nicolas.lira@alma.cl

Iris Nijman
Public Information Officer
National Radio Astronomy Observatory Charlottesville, Virginia - USA
Cell phone: +1 (434) 249 3423
Email: alma-pr@nrao.edu

Bárbara Ferreira
ESO Public Information Officer
Garching bei München, Germany
Phone: +49 89 3200 6670
Email: pio@eso.org

Masaaki Hiramatsu
Education and Public Outreach Officer, NAOJ Chile
Observatory
, Tokyo - Japan
Phone: +81 422 34 3630
Email: hiramatsu.masaaki@nao.ac.jp

---