Unusually bright light in the sky that appeared suddenly last June has got astronomers in great excitement. After months of study, they still aren’t sure what the object — universally referred to as the “Cow” — is. Whatever it is, says astronomer Liliana Rivera Sandoval of Texas Tech University in Lubbock, “It’s super strange.”
The Cow first appeared in telescope observations on 16 June 2018, in what turned out to be a small galaxy (星系) about 200 million light years away. “When we saw that we thought, let’s get on this,” says Daniel Perley, an astronomer at Liverpool John Moores University.
The early observations confirmed the Cow was truly strange. It didn’t show the obvious changes in its light output that an exploding star would make. Sandoval says as soon as she and colleagues knew the Cow was truly distant, they requested time on NASA’s Neil Gehrels Swift Observatory to see what the Cow was doing in X-rays. Although the X-ray brightness varied over the early weeks, “the spectrum (光谱) didn’t change, which is very unusual,” she notes. After 3 weeks, the X-ray signal began to vary more wildly while also dropping off in brightness.
Many astronomers agree that the long and steady duration of the event means that it was powered after an initial explosion by some form of central engine. But what that engine may be is also far from clear. Some argue that it could be a very unusual star whose central part has collapsed (坍塌) inward after it exploded. Others say it is a tidal disruption event — a star being torn apart by a black hole. But that usually requires the supermassive black hole in the center of a galaxy, and the Cow is situated in its galaxy’s arm. So, some say, it could be a tidal disruption event generated by an intermediate mass black hole, although evidence for the existence of such smaller black holes remains controversial. “All explanations have problems,” Sandoval says, “I hope there are more Cows.”
【小题1】What is astronomers’ main concern about the Cow?| A．What it is. | B．How it forms. |
| C．When it appears. | D．Where it is from. |
| A．What the Cow was doing. |
| B．How far the Cow is from the earth. |
| C．Whether the Cow is an exploding star. |
| D．Why the X-ray signals varied wildly. |
| A．The research results help little. |
| B．More Cows will appear. |
| C．Extra attention should be paid to the Cow. |
| D．More information is needed. |
| A．A Strange Explosion in Deep Space |
| B．An Interesting Observation of NASA |
| C．A Wide Range of Changes in the Galaxies |
| D．A Great Achievement in Astronomy |
