NASA studies mysterious blast
Two teams argue that it is either a black hole shredding a passing star or it is a supernova
Abrief and unusual flash spotted in the night sky on June 16, 2018, puzzled astronomers and astrophysicists across the globe. The event — called AT2018cow and nicknamed “the Cow” after the coincidental final letters in its official name — is unlike any celestial outburst saw before, prompting multiple theories about its source.
Over three days, the Cow produced a sudden explosion of light at least 10 times brighter than a typical supernova, and then it faded over the next few months. This unusual event occurred inside or near a star-forming galaxy known as CGCG 137068, located about 200 million light-years away in the constellation Hercules. The Cow was first observed by the NASA-funded Asteroid Terrestrial-impact Last Alert System telescope in Hawaii.
So exactly what is the Cow? Using data from multiple NASA missions, including the Neil Gehrels Swift Observatory and the Nuclear Spectroscopic Telescope Array (NuSTAR), two groups are publishing papers that provide possible explanations for the Cow’s origins. One paper argues that the Cow is a monster black hole shredding a passing star. The second paper hypothesizes that it is a supernova — a stellar explosion — that gave birth to a black hole or a neutron star.
Researchers from both teams shared their interpretations at a panel discussion on Thursday, at the 233rd American Astronomical Society meeting in Seattle.
The zoomedin image shows the location of the “Cow” in the galaxy
A Black Hole Shredding a Compact Star?
One potential explanation of the Cow is that a star has been ripped apart in what astronomers call a “tidal disruption event.” Just as the Moon’s gravity causes Earth’s oceans to bulge, creating tides, a black hole has a similar but more powerful effect on an approaching star, ultimately breaking it apart into a stream of gas. The tail of the gas stream is flung out of the system, but the leading edge swings back around the black hole collides with itself and creates an elliptical cloud of material. According to one research team using data spanning from infrared radiation to gamma rays from Swift and other observatories.
Or a New View of a Supernova?
If we’re seeing the birth of a compact object in real time, this could be the start of a new chapter in our understanding of stellar evolution Brian Grefenstette, NuSTAR instrument scientist at Caltech
A different team of scientists was able to gather data on the Cow over an even broader range of wavelengths, spanning from radio waves to gamma rays. Based on those observations, the team suggests that a supernova could be the source of the Cow. When a massive star dies, it explodes as a supernova and leaves behind either a black hole or an incredibly dense object called a neutron star. The Cow could represent the birth of one of these stellar remnants.