Posted on January 11, 2019
"We know from the theory that black holes and neutron stars form when a star dies, but we have never got it right seen after they are born. No way! Said Raffaella Margutti, Assistant Professor of Physics and Astronomy at Northwestern University, about the mysterious bright object that astronomers called "The Cow." "A" light bulb "was sitting deep in the blast, it would have been difficult to see this in a normal starburst, but the cow had very little ejection mass, which allowed us to directly see the radiation from the central engine."
With the help of the WM Keck Observatory on Maunakea, Hawaii and the ATLAS of the University of Hawaii In both telescopes, the multi-institutional team has evidence that they have probably captured precisely the moment when a star becomes a compact object
The cow pictured above is only visible as one of two bright spots in the lower right quadrant of the CGCG 137-068 classified spiral galaxy.
The debris of the stars, which adjusts to the event horizon of the object approaching and whirling around it caused the remarkably bright sparkle.The research that will appear in the Astrophysical Journal became announced today at a press conference at the 233rd meeting of the American Astronomical Society in Seattle.
This rare event will help astronomers better understand physics in the first moments of the creation of a black hole or a neutron star.
"Dark Hearts of the Cosmos" – Iridescent New Mergers of Black Holes and Neutron Stars
"Due to its X-ray and UV radiation, The Cow seems to have been caused by a black hole devouring a white dwarf. Further observations of other wavelengths across the spectrum led to our interpretation that "The Cow" is indeed the formation of an accentuating black hole or neutron star, "said lead author Margutti, a faculty member of Northwestern CIERA (Center for Interdisciplinary Exploration and Research) for Astrophysics)
The cow was first discovered on June 16 after the ATLAS telescopes captured a spectacularly bright anomaly in the Hercules constellation on Haleakala and Maunaloa 200 million light-years away, and the object quickly flared up and then almost vanished just as fast.
The event immediately attracted international interest and left astronomers scratching their heads. "We thought it must be a supernova," said Margutti, "but what we observed questioned our present beliefs about star death."
"An Illusion?" – ESO image of the supermassive black hole of the milk road
First, the anomaly was unnaturally bright – 10 to 100 times brighter than a typical supernova. It flared up and vanished much faster than other known starbursts, 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 released most of its energy. In a universe where some phenomena last millions and billions of years, two weeks are just a blink of an eye.
"We knew instantly that within a few days, this source became the peak luminance of the inactive phase," said co-author Ryan Chornock, Assistant to Physics and Astronomy at Ohio University. "That was enough to get everyone excited because it was so unusual and very close for astronomical reasons."
Through access from Northwestern to Keck Observatory's double telescopes, Margutti's team examined the make-up of the object with the Low Resolution Imaging Spectrometer ( LRIS) at the Keck I Telescope and the DEep Imaging and Multi-Object Spectrograph (DEIMOS) at the Keck II.
author Nathan Roth, JSI postdoctoral fellow at the University of Maryland. "Keck's unique niche is the ability to oversee the later behavior of The Cow. That can be difficult; The more time passes after the event, the weaker it becomes. However, with Keck's late spectroscopy, we were able to penetrate the "interiors" of the explosion. This showed that the red-shifted spectral features of AT2018cow were very visible. "
" The cow is a prime example of a kind of observation that becomes critical in astronomy: quick response to transient events, "says John O'Meara, chief scientist at Keck Observatory. "Looking to the future, we are implementing new observation strategies and telescopic instruments that will allow us to be as fast as possible in the sky and in science."
The team also received optical images from the MMT Observatory in Arizona as the SOAR telescope from Southern Astrophysical Research in Chile.
When Margutti and her team studied The Cow's chemical composition, they found clear evidence of hydrogen and helium, precluding models of compact objects producing gravitational waves.  "It took a while for us to know what we were looking at, I would say months," said Brian Metzger, associate physics professor at Columbia University. "We tried several options and had to return to the drawing board several times. Thanks to the hard work of our incredibly dedicated team we were finally able to interpret the results.
Astronomers have traditionally investigated stellar fatalities in optical wavelength using telescopes to capture visible light.
Margutti's team on the other hand uses a more comprehensive approach. After ATLAS discovered the object, Margutti's team quickly conducted follow-up observations using multiple observatories to analyze the cow at different wavelengths.
Researchers viewed the object in hard X-rays using NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) and the European Space Agency's International Gamma-Ray Astrophysics Laboratory (ESA) (INTEGRAL), using soft X-rays (the 10 times stronger than normal X-rays) with the X-ray multi-mirror mission (XMM-Newton) of the ESA and in radio waves with the Very Large Array (VLA) of the National Radio Astronomy Observatory (NRAO). This allowed them to further investigate the anomaly long after the initial visible brightness faded.
Margutti cites the relative nakedness of the cow to possibly solve this intergalactic mystery. Although stars may constantly collapse into black holes, the large amount of material surrounding newborn black holes blocks the astronomers' view.
Luckily, around 10 times fewer litter swirled around the cow compared to a typical starburst. Due to the lack of material, astronomers could 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 star's relative proximity to Earth. Although embedded in the distant dwarf galaxy called CGCG 137-068, astronomers see it as "just around the corner."
"Two hundred million light-years are close to us," said Margutti. "This is the closest temporary object of this kind we have ever found."
The daily galaxy over the Keck Observatory