Nav: Home

Birth of a black hole or neutron star captured for the first time

January 10, 2019

Maunakea, Hawaii - A Northwestern University-led international team of astronomers is getting closer to understanding the mysterious bright object that burst in the northern sky this summer, dubbed AT2018cow or 'The Cow.'

With the help of W. M. Keck Observatory on Maunakea, Hawaii and the University of Hawaii Institute for Astronomy's ATLAS twin telescopes, the multi-institutional team now has evidence that they likely captured the exact moment a star collapsed to form a compact object, such as a black hole or neutron star.

The stellar debris, approaching and swirling around the object's event horizon, caused the remarkably bright glow. The research, which will be appearing in The Astrophysical Journal, was announced today during a press conference at the 233rd Meeting of the American Astronomical Society in Seattle.

This rare event will help astronomers better understand the physics at play within the first moments of the creation of a black hole or neutron star.

"Based on its X-ray and UV emission, 'The Cow' may appear to have been caused by a black hole devouring a white dwarf. But further observations of other wavelengths across the spectrum led to our interpretation that 'The Cow' is actually the formation of an accreting black hole or neutron star," said lead author Raffaella Margutti, assistant professor of physics and astronomy at Northwestern University and faculty member of Northwestern's CIERA (Center for Interdisciplinary Exploration and Research for Astrophysics). "We know from theory that black holes and neutron stars form when a star dies, but we've never seen them right after they are born. Never."


The Cow was first spotted on June 16 after the ATLAS telescopes on Haleakala and Maunaloa captured a spectacularly bright anomaly 200 million light years away in the Hercules constellation. The object quickly flared up, then vanished almost as quickly.

The event captured immediate international interest and left astronomers scratching their heads. "We thought it must be a supernova," Margutti said. "But what we observed challenged our current notions of stellar death."

For one, the anomaly was unnaturally bright -- 10 to 100 times brighter than a typical supernova. It also flared up and disappeared much faster than other known star explosions, with particles flying at 30,000 kilometers per second (or 10 percent of the speed of light).

Within just 16 days, the object had already emitted most of its power. In a universe where some phenomena last for millions and billions of years, two weeks amounts to the blink of an eye.

"We knew right away that this source went from inactive to peak luminosity within just a few days," said co-author Ryan Chornock, assistant physics and astronomy professor at Ohio University. "That was enough to get everybody excited because it was so unusual and, by astronomical standards, it was very close by."

Using Northwestern's access to Keck Observatory's twin telescopes, Margutti's team took a closer look at the object's makeup with the Low Resolution Imaging Spectrometer (LRIS) on the Keck I telescope as well as the DEep Imaging and Multi-Object Spectrograph (DEIMOS) on Keck II.

"Keck was instrumental in determining the chemical composition and geometry of AT2018cow," said co-author Nathan Roth, a JSI postdoctoral fellow at the University of Maryland. "Keck's unique niche is its capability to monitor the late-time behavior of The Cow. This can be difficult; as more time passes after the event, the fainter it becomes. But with Keck's late time spectroscopy, we were able to pierce through the 'interiors' of the explosion. This revealed AT2018cow's red-shifted spectral features very nicely."

"The Cow is a great example of a type of observation that's becoming critical in astronomy: rapid response to transient events," says Keck Observatory Chief Scientist John O'Meara. "Looking forward, we are implementing new observational policies and telescope instrumentation that allow us to be as quick on the sky and to the science as we can." 

The team also obtained optical images from the MMT Observatory in Arizona, as well as the Southern Astrophysical Research SOAR Telescope in Chile.

When Margutti and her team examined The Cow's chemical composition, they found clear evidence of hydrogen and helium, which excluded models of compact objects merging -- like those that produce gravitational waves.

"It took us a while for us to realize what we were looking at, I would say months," said co-author Brian Metzger, associate physics professor at Columbia University. "We tried several possibilities and were forced to go back to the drawing board multiple times. We were finally able to interpret the results, thanks to the hard work of our incredibly dedicated team."

In addition to Chornock, Roth, and Metzger, Margutti's core team also includes Indrek Vurm, senior research fellow at Tartu Observatory, as well as Northwestern CIERA postdoctoral researchers Giacomo Terreran, Deanne Coppejans, and Kate Alexander.


Astronomers have traditionally studied stellar deaths in the optical wavelength, which uses telescopes to capture visible light.

Margutti's team, on the other hand, used a more comprehensive approach. After ATLAS spotted the object, Margutti's team quickly conducted follow-up observations using multiple observatories to analyze The Cow in different wavelengths.

The researchers viewed the object in hard X-rays using NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) and the European Space Agency's (ESA) INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL), in soft X-rays (which are 10 times more powerful than normal X-rays) using ESA's X-ray Multi-Mirror Mission (XMM-Newton), and in radio waves using National Radio Astronomy Observatory's (NRAO) Very Large Array (VLA).

This enabled them to continue studying the anomaly long after its initial visible brightness faded.

Margutti attributes The Cow's relative nakedness to potentially unraveling this intergalactic mystery. Although stars might collapse into black holes all the time, the large amount of material around newly born black holes blocks astronomers' vision.

Fortunately, about 10 times less ejecta swirled around The Cow compared to a typical stellar explosion. The lack of material allowed astronomers to peer straight through to the object's "central engine," which revealed itself as a probable black hole or neutron star.

"A 'lightbulb' was sitting deep inside the ejecta of the explosion," Margutti said. "It would have been hard to see this in a normal stellar explosion. But The Cow had very little ejecta mass, which allowed us to view the central engine's radiation directly."


Margutti's team also benefited from the star's relative closeness to Earth. Even though it was nestled in the distant dwarf galaxy called CGCG 137-068, astronomers consider that to be "right around the corner."

"Two hundred million light-years is close for us," Margutti said. "This is the closest transient object of this kind that we have ever found."

"Being given the opportunity to contribute to something as cutting edge and international as understanding AT2018cow as an undergrad is a surreal experience," said co-author Daniel Brethauer, a first-year undergraduate student at Northwestern. "To have helped the world's experts figure out what AT2018cow is even in the smallest way was beyond my wildest expectations at the beginning of the summer and something that I will remember for the rest of my life."

The Low Resolution Imaging Spectrometer (LRIS) is a very versatile visible-wavelength imaging and spectroscopy instrument commissioned in 1993 and operating at the Cassegrain focus of the Keck I telescope. Since it has been commissioned, it has seen two major upgrades to further enhance its capabilities: addition of a second blue arm optimized for shorter wavelengths of light and the installation of detectors that are much more sensitive at the longest (red) wavelengths. Each arm is optimized for the wavelengths it covers. This large range of wavelength coverage, combined with the instrument's high sensitivity, allows the study of everything from comets (which have interesting features in the ultraviolet part of the spectrum), to the blue light from star formation, to the red light of very distant objects. LRIS also records the spectra of up to 50 objects simultaneously, especially useful for studies of clusters of galaxies in the most distant reaches, and earliest times, of the universe. LRIS was used in observing distant supernovae by astronomers who received the Nobel Prize in Physics in 2011 for research determining that the universe was speeding up in its expansion.


The DEep Imaging and Multi-Object Spectrograph (DEIMOS) boasts the largest field of view (16.7arcmin by 5 arcmin) of any of the Keck Observatory instruments, and the largest number of pixels (64 Mpix). It is used primarily in its multi-object mode, obtaining simultaneous spectra of up to 130 galaxies or stars. Astronomers study fields of distant galaxies with DEIMOS, efficiently probing the most distant corners of the universe with high sensitivity.


The W. M. Keck Observatory telescopes are the most scientifically productive on Earth. The two, 10-meter optical/infrared telescopes atop 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. 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 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. 

W. M. Keck Observatory

Related Black Hole Articles:

Scientists make waves with black hole research
Scientists at the University of Nottingham have made a significant leap forward in understanding the workings of one of the mysteries of the universe.
Collapsing star gives birth to a black hole
Astronomers have watched as a massive, dying star was likely reborn as a black hole.
When helium behaves like a black hole
A team of scientists has discovered that a law controlling the bizarre behavior of black holes out in space -- is also true for cold helium atoms that can be studied in laboratories.
Star in closest orbit ever seen around black hole
Astronomers have found evidence of a star that whips around a likely black hole twice an hour.
Tail of stray black hole hiding in the Milky Way
By analyzing the gas motion of an extraordinarily fast-moving cosmic cloud in a corner of the Milky Way, Astronomers found hints of a wandering black hole hidden in the cloud.
Hubble gazes into a black hole of puzzling lightness
The beautiful spiral galaxy visible in the center of the image is known as RX J1140.1+0307, a galaxy in the Virgo constellation imaged by the NASA/ESA Hubble Space Telescope, and it presents an interesting puzzle.
Clandestine black hole may represent new population
Astronomers have combined data from NASA's Chandra X-ray Observatory, the Hubble Space Telescope and the National Science Foundation's Karl G.
When will a neutron star collapse to a black hole?
Astrophysicists from Goethe-University Frankfurt have found a simple formula for the maximum mass of a rotating neutron star and hence answered a question that had been open for decades.
Behemoth black hole found in an unlikely place
Astronomers have uncovered a near-record breaking supermassive black hole, weighing 17 billion suns, in an unlikely place: in the center of a galaxy in a sparsely populated area of the universe.
Behemoth black hole found in an unlikely place
Astronomers have uncovered one of the biggest supermassive black holes, with the mass of 17 billion Suns, in an unlikely place: the centre of a galaxy that lies in a quiet backwater of the Universe.

Related Black Hole Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Climate Crisis
There's no greater threat to humanity than climate change. What can we do to stop the worst consequences? This hour, TED speakers explore how we can save our planet and whether we can do it in time. Guests include climate activist Greta Thunberg, chemical engineer Jennifer Wilcox, research scientist Sean Davis, food innovator Bruce Friedrich, and psychologist Per Espen Stoknes.
Now Playing: Science for the People

#527 Honey I CRISPR'd the Kids
This week we're coming to you from Awesome Con in Washington, D.C. There, host Bethany Brookshire led a panel of three amazing guests to talk about the promise and perils of CRISPR, and what happens now that CRISPR babies have (maybe?) been born. Featuring science writer Tina Saey, molecular biologist Anne Simon, and bioethicist Alan Regenberg. A Nobel Prize winner argues banning CRISPR babies won’t work Geneticists push for a 5-year global ban on gene-edited babies A CRISPR spin-off causes unintended typos in DNA News of the first gene-edited babies ignited a firestorm The researcher who created CRISPR twins defends...