Published on 11 January 2019
"We know from the theory that black holes and neutron stars are formed when a star dies, but we have never seen them well after they were born Never! "Said Raffaella Margutti, assistant professor of physics and astronomy at Northwestern University on the mysterious luminous object that has confounded astronomers nicknamed" The Cow ". "A" light bulb "was sitting deeply inside the explosion.It would have been difficult to see it in a normal stellar explosion.But The Cow had very little mass of ejecta, which allowed us to see directly the radiations of the central engine. "
With the help of the WM Keck Observatory on Maunakea, Hawaii and the University of Hawaii Institute for Astronomy & # 39; s ATLAS the twin telescopes, the multi team – Institutional now has evidence that they have probably captured the exact moment when a star collapsed to form a compact object, such as a black hole or a neutron star.
The cow shown in the image above is barely visible as one of the two bright spots in the lower right quadrant of the spiral galaxy classified as CGCG 137-068.
Star debris, approaching and swirling around the object's event horizon, caused a noticeably bright glow. The research, which will appear on 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 in the first moments of the creation of a black hole or neutron star.
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"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 lengths Wave through the spectrum have led to our interpretation that "The Cow" is actually forming a captivating black hole or neutron star, "said principal author Margutti, a member of the Northwestern CIERA faculty (Center for Interdisciplinary Exploration and Research for Astrophysics) ..
The Cow was spotted for the first time on June 16 after the ATLAS telescopes on Haleakala and Maunaloa captured an anomaly extraordinarily brilliant at 200 million light years in the constellation of Hercules. The object lit quickly, then vanished almost as quickly.
The event immediately captured international interest and left astronomers scratching their heads. "We thought it was a supernova," said Margutti. "But what we have observed has challenged our current notions of stellar death."
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For one, the anomaly was unnaturally brilliant – 10 to 100 times brighter than a typical supernova. It also exploded and disappeared much faster than other known stellar explosions, with particles flying at 30,000 kilometers per second (or 10% of the speed of light).
In just 16 days, the object had already issued most of its power. In a universe where some phenomena last for millions and billions of years, the two weeks amount to a blink of an eye.
"We knew immediately that this source went from idle to peak brightness in a few days," said co-author Ryan Chornock, professor of physics and astronomy at the University of Ohio. "It was enough to excite everyone because it was so unusual and, by astronomical standards, it was very close."
Using Northwestern access to the Keck Observatory twin telescopes, Margutti's team took a closer look at the trick of the object Low Resolution Imaging Spectrometer (LRIS) on the Keck telescope I as well as DEEPOS (DEEP Imaging and Multi-Object Spectrograph) 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. "The unique niche of Keck is its ability to monitor the late behavior of The Cow. This can be difficult, the more time passes after the event, the weaker it becomes.But with Keck's late spectroscopy, we have been in able to penetrate through the "interiors" of the explosion.This revealed very well the spectral characteristics of the red of AT2018cow. "
" The Cow is a great example of a type of observation that is becoming critical in astronomy: rapid response to transient events, "says John O & # 39; Meara, Chief Scientist of the Keck Observatory. "Looking ahead, we are implementing new telescope observation and instrumentation policies that allow us to be as fast as possible in the sky and in science."
The team also obtained optical images from the MMT observatory in Arizona, as well as the SOAR Telescope on southern astrophysics research in Chile.
When Margutti and his team examined the chemical composition of the cow, they found clear tests of hydrogen and helium, which excluded models of compact objects that joined together – like those that produce gravitational waves.  "It took us a while to understand what we were looking at, I would say months," said co-author Brian Metzger, an associate professor of physics at Columbia University. "We have tried different possibilities and we have been forced to return to the drawing board several times and we have finally been able to interpret the results, thanks to the hard work of our incredibly dedicated team.
Astronomers have traditionally studied stellar deaths in length optical wave, which uses telescopes to capture visible light.
Margutti's team, on the other hand, used a more complete approach, after which ATLAS identified the object , the Margutti team quickly conducted follow-up observations using multiple observatories to analyze The Cow in different wavelengths.
Researchers looked at the object in harsh X-rays using NASA Nuclear Spectroscopic Telescope Array (NuSTAR) and Europe INErnational gamma-ray astrophysics laboratory (ESA) (INTEGRAL), in soft X-rays (which are 10 times more powerful than normal X-rays) using the Multi-mirror X-ray mission of the ESA (XMM-Newton), and in radio waves using the Array Very Large Array (VLA) of the National Radio Astronomy Observatory (NRAO). This allowed them to continue studying the anomaly long after its initial visible brightness had faded.
Margutti attributes the relative nudity of the Cow to a potential misuse of this intergalactic mystery. Although the stars can continuously collapse into black holes, the large amount of material around the newly born black holes blocks astronomers' vision.
Fortunately, about 10 times less Ejecta revolved around The Cow compared to a typical stellar explosion. The lack of material allowed the astronomers to look directly at the "central engine" of the object, which turned out to be a probable black hole or neutron star.
Margutti's team also benefited from the relative proximity of the star to the Earth. Although it was in the distant dwarf galaxy called CGCG 137-068, astronomers believe it is "just around the corner".
"Two hundred million light years are close for us," said Margutti. "This is the closest transient object of this kind we've ever found."
The Daily Galaxy via Keck Observatory