The Last Asteroid Earth Impact Alert System detected something highly unusual on June 16, 2018. The discovery of a strange burst in the sky, which is illuminated and vanished, was reported in an astronomical telegram, which then alerted scientists . The source was named AT2018cow, based on a naming convention for transient sources where the last three letters are badigned randomly. Understandably, however, the scientists quickly dubbed it "the Cow."
Astronomers from all over the world began to observe the Cow, which is one of the strangest and most observed objects that have recently been discovered. The measurements of its brightness and wavelength suggest that it is about 200 m away from our own galaxy. This means that the explosion would have been extremely bright to have been detected, producing as much energy as solar radiation in 1,700 years.
Today, there is a race to find out exactly what it is. Our new research, which will be published in the Monthly Notices of the Royal Astronomical Society, has given an explanation.
The Cow must have appeared extremely suddenly, it was not seen in a search only 32 hours before. Follow-up observations using instruments in space and on the ground suggested that its brightness was larger than expected from a supernova (an exploding star). An explosion of gamma rays (an intense explosion of light) would have been another possibility, but the X-ray emission that accompanies the event seemed too small to fit this description.
The temperature profile of the source indicated that the object shone at a temperature of approximately 26,000 ° C, with a maximum brightness in the ultraviolet region of light. Assuming that the brightness of such a thermal source was a sphere, the size turned out to be very large: approximately 50 times the Earth's orbit around the Sun. A supernova would also spread to something similar in size.
A second surprise was that the spectrum, a measure of how light decays according to wavelength, did not show the same characteristics as a typical supernova. It was like the glow of a hot body only. Some weak but wide shots and jumps suggested that there was, however, some material that emits at an extremely high speed in a glowing cocoon around the body.
As a member of the Neil Gehrels Swift observatory team (shortly, "Swift"), I was asked to research our data for more information. Swift is a satellite in a low Earth orbit that can point to a new source automatically in about 90 seconds after a gamma ray burst, or after being ordered to do so from the ground. Swift has many telescopes and can provide data in a range of different regions of light, from visible and ultraviolet rays to gamma rays.
At that time, several other teams were investigating the source using several observatories. The documents based on the Swift X-ray data and the ATLAS data had already been published. Dan Perley, from John Moores University in Liverpool, and his collaboration had just finished Herculean's task of badyzing the optical and infrared data of the great collaboration GROWTH, which includes telescopes around the world, and tracking interesting sources.
In the last weeks of August, all this research had made it clear that the Vaca definitely did not fit the profile of a normal gamma-ray burst, nor a supernova or a super-bright supernova (an extremely bright supernova). However, this left the possibility that what we were seeing was a star that was being shattered by a black hole, the so-called interruption of the tides.
This possibility became a focus of our investigation. With the Swift data of multiple wavelength in the hand, and with preprints already published that provide additional information in certain wavelengths of light, we had the opportunity to limit the search.
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We decided to combine well understood physics with observations, how to use the distance at which a black hole swallows an entire star, the distance at which a black hole separates a star, and on that basis we wrote our article. We suggest that a white dwarf (a star that has reached the end of its useful life) of 0.1 or 0.4 times the mbad of the sun that is being destroyed by a black hole of 100,000 to a million solar mbades could explain what What we see . In fact, this would coincide with observations measured in various regions of light, from gamma rays to radio waves. Such an event would also provide a natural means to form the jet of material that was observed.
But there are other possibilities. Two recent articles directed by Anna Ho de Caltech and Rafaella Margutti of Northwestern University respectively suggest that the Vaca was an "engine-driven" explosion in which a fast-spinning neutron star (a very dense star) formed in an exotic form of supernova was pumping energy into the expanding material. This research also leaves open the possibility that it is a black hole pumping.
Unfortunately, we missed the first stages of the event, which may have contained clues as to which process can actually generate huge amounts of energy. With luck, with more and better telescopes guarding the sky, we can detect similar events in earlier times in the future.
An object like this can also be a source of gravitational waves: ripples in space-time. That means observatories like the LISA satellite that the European Space Agency is building now can really see them. Holy cow, that would be incredible.
This article appeared for the first time in The conversation.