The COW in Space

You probably saw all the hoo-rah last week about a COW-like object in space that has astronomers “mystified”, or “baffled”, or even “stumped” (according to the breathless headlines on various news sites. So, what’s behind the headlines that are milking the story for all its worth?

Making a COW

Let’s start with the name of this thing that astronomers observed. The full name of the object is AT2018cow, and you can see the discovery image here. It erupted in or near a galaxy known as CGCG 137-068. That’s located about 200 million light-years away in the constellation Hercules. This shows the location of the “Cow” in the distant galaxy.

Think of it as some kind of eruption in a star, not unlike a supernova or other such outburst. These happen fairly frequently. Astronomers give them complicated names based on what instrument is used to observe them. The name also includes WHEN they’re found. This one was found by the Asteroid Terrestrial-impact Last Alert survey telescope in Hawaii. That’s where the letters AT come from. 2018 is the year it was discovered, and each time there’s one found, it is followed by a letter or sequence of letters. In this case, the sequence came up “cow”.

Astronomers being astronomers, it got shortened to “The Cow” and that led to a lot of really bad puns at last week’s AAS meeting that I won’t repeat here, but some of them were actually funny.

What IS “The COW”?

Now that we’ve got the name out of the way, let’s talk about what this event could have been. I say that because it’s still not clear EXACTLY what happened to cause this bright outburst. That’s going to take some more study and observations. But, there are some leading theories about what The COW outburst was.

First, it could have been the outburst of energy from a black hole shredding a nearby compact star. This is what astronomers call a “tidal disruption event” and could release tremendous amounts of energy that can be detected across large distances. If this happened, then it’s likely that a black hole’s gravity had a close encounter with a star that happened to be passing by. AS they danced past each other, the gravitational pull of the black hole disrupted the star and stretched it into a huge stream of superheated gas. As the gravitational dance continues, the end of the stream whips around like a tail and collides with itself. That creates another superheated cloud of material that would glow quite brightly.

It’s possible that the star was a white dwarf. When it encountered the 100,000-solar mass black hole, that’s what caused all the fireworks. There are still a lot of questions to be answered about this possible cause for The Cow, including its exact location and more details about the star and its black hole dance partner.

An Idea from Supernova Science

Other scientists observing The COW have a different idea, based on their observations from multiple types of instruments. They think that a supernova could have been the culprit that kicked The COW into action. Given the span of observations ranging from gamma rays to radio frequencies, the second team thinks that what they and others observed was the earliest throes of the creation of a compact massive body (like a neutron star or a black hole) as part of a supernova explosion. Nobody’s actually observed one these before, so it would be the first of its kind.

Observing The COW

So, how did astronomers get a glimpse of this thing? First, of course, it showed up in the AT survey. That’s actually a sky survey designed to look for possible asteroids and other impactors that could threaten Earth. It will detect anything that flares up in the sky, and even a distant explosion like The COW qualifies.

After that discovery, astronomers used a multi-wavelength set of observatories to do follow-up observations. Here’s a list:

• Neil Gehrels Swift Observatory
• Nuclear Spectroscopic Telescope Array
• XMM-Newton
• the Very Large Array
• INTEGRAL satellite.

To learn more, check out this video from NASA.

These observatories are sensitive to a range of light from radio frequencies to x-rays and gamma-rays. They’re designed to look at fast-occurring energetic objects and events in the universe.

Astronomers will continue to study the data these instruments provided about The COW to figure out just what scenario fits the data best: a gravitational dance between black hole and star or a supernova explosion creating a new high-mass object? Either answer would advance our understanding of stellar physics and evolution. And, as with most science, there’s a healthy amount of debate about the strength of the explosion and other aspects of the event.

Stay tuned! To learn more, check out this video from NASA.

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