Ambulances, Tatooine, and tall people: explaining Pitt professor's discovery of smallest known black hole as best we can | News | Pittsburgh | Pittsburgh City Paper

Ambulances, Tatooine, and tall people: explaining Pitt professor's discovery of smallest known black hole as best we can

click to enlarge 2MASS J05215658+4359220 (the one at the very center with a red cross over it) - IMAGE: PAN-STARRS SURVEY
2MASS J05215658+4359220 (the one at the very center with a red cross over it)

The concept of black holes is notoriously complicated, so when it comes to explaining them to laypeople or City Paper writers, it helps to have a handful of metaphors on deck.
In this regard, Carles Badenes, an associate professor in the Department of Physics and Astronomy at the University of Pittsburgh, has quite the arsenal. Along with a team of researchers from Ohio State University, Badenes recently discovered the smallest black hole ever known. The process was rigorous and convoluted, which is where the metaphors can help.

At its simplest level, the process starts with the Doppler effect, which Badenes explains as the phenomenon when the pitch of an ambulance's siren changes as it moves toward you or away from you (metaphor No. 1). But the effect exists with light in space, too. When observing a star, Badenes and crew studied the wavelengths (colors) being emitted and, using the Doppler principle, deduced when a star was moving closer to them (blue) or farther away (red). Badenes called this research a "fishing expedition" (No. 2). If stars displayed the phenomenon in a relatively periodic or predictable way, one could conclude that the star is in some kind of orbit around a binary companion.

OK, a binary companion or "binary system" is when two or more stars revolve around a common center. Metaphor No. 3: "This would be very similar to the planet Tatooine in Star Wars, where Luke Skywalker sees two suns setting — that’s a binary star," says Badenes. "If you were very far away from the Tatooine system, you would see the lights of the lines of these stars moving toward the red and the blue with a certain frequency, which is essentially the binary period of the orbit."

But when it came to one particular star, 2MASS J05215658+4359220, Badenes and his colleagues found that the binary companion did not emit any light and inferred that the unknown object had a mass at least three times the Earth's sun. Using a process of elimination — for various reasons, the unknown mass couldn't be a neutron star or white dwarf — they concluded that it was a black hole.

This discovery is significant and cool for a number of reasons, but most notably, black holes are not normally found this way. Traditionally, black holes are studied by "watching them eat" (mini metaphor). They're in a process known as accretion, meaning that materials are falling into a black hole that does not emit any light but in the process of being "eaten," the materials get hot and give off light. So the easiest way to find black holes was to look for light being emitted in this way. But Badenes says this process is biased and explains it with metaphor No. 4:

"Imagine that you’re trying to figure out how tall, on average, the students of the University of Pittsburgh are and it occurs to you to measure students' heights in the men’s locker room after the basketball team is done training. You’re going to come out of that locker room thinking that all the students at Pitt are very tall and that’s just not true. It’s because you were measuring the tall ones that you got that number, right?"

(Quick aside, Badenes used this same explanation nearly verbatim in his interview with the Post-Gazette, but that's probably because it works.)

Basically, the brighter black holes are easier to find because they're massive, so the majority of black holes found tend to be massive.
The discovery of this black hole "opens the door for discovering and studying black holes while they’re still hidden in the shadows of the cosmos before they consume matter and become luminous sources."

To get a (slightly) simpler explanation of this discovery and the nature of his work, Pittsburgh City Paper reached out to Badenes for more information.


The name of this star is 2MASS J05215658+4359220. Everything after 2MASS, those are coordinates, right? Like longitude and latitude?
That’s exactly what it is. But they’re not longitude and latitude, they're what we call "right ascension" and "declination," but it’s the same idea. The reason we use these names is because anyone can go to a digital map of the sky and enter those coordinates and they will be able to find the star.

How far away is this star?
This star is about 3000 parsecs away. In layman’s terms, it’s about 10,000 light-years away.



What else can you tell me about 2MASS?

This star is what we call a red giant, relatively large in size and quite luminous—about a couple hundred times as luminous as our own sun, and quite a bit colder. The surface temperature of the sun is around 6,000 degrees Kelvin [more than 10,000 degrees Fahrenheit], and this star has a surface temperature of around 4,000 degrees K, so it would appear quite a bit redder.

The black hole near 2MASS is the smallest known?

It’s the least massive black hole known for now.

So mass is the unit, not "massive" in the colloquial sense.

The thing is so small that we’re never going to see it. Do you remember a few months ago the first picture of a black hole ever was released? That’s also a black hole, but it’s what’s called a supermassive black hole — it has millions of times the mass of the sun. So that makes it physically much larger, so you can see the shadow of the black hole against the bright material that surrounds it. But this thing is just a few miles across and it’s 10,000 light-years away, so we’re never going to see it.

Even those with a passing interest in science or space seem to love black holes. Why do you think that is?

Black holes are one of the great examples of the success of things like physics, general relativity in this particular case. They’re very extreme objects, they don’t behave like anything we know. Black holes emit no light, they have a very large mass, the space-time gets completely warped around them. They’re really alien objects in the sense that they don’t behave like anything we’re used to. That’s essentially what fascinates people.

I should mention that many depictions of black holes in science fiction movies are completely unrealistic, they are not cosmic vacuum cleaners that are sucking everything up all the time. That’s not what’s going on at all. But they do have some properties that are very strange and extremely bizarre. Like time does slow down quite a bit when you get close to a black hole. Then there’s this idea of event horizon, there’s a distance from a black hole, and the case of this particular black hole it’s just a few miles, but if you get close enough you can never leave. That’s part of the allure.

It does work well for science fiction.

Some depictions are better than others. 

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