Is that a quasar or are you just showing your asteroid?

June 6, 2023   Issue #574

Astro Tidbit

A brief synopsis of some interesting astronomy/science news

Here’s a thing about science: Sometimes you come to the wrong conclusion. That can happen a lot of ways! The data might not be sufficient to let you know you’re down the wrong path. You might be biased (hoo boy have I seen that). You might simply be misinterpreting the data. Or the data themselves may be off for some reason.

We may have a case of the latter: Astronomers just published a paper claiming that the discovery of an extremely distant quasar is actually no such thing. Instead, the original observations were contaminated by, of all things, a passing asteroid!

OK, a bit of explanation. We think all big galaxies have huge black holes in their cores. If material is falling onto that black hole it gets very hot before it falls in, and emits a lot of light. A lot of factors play into what we see from such an active galaxy, including the amount of material falling in, the mass of the black hole, the geometry we see it, and more. Quasars are one of these many kinds of galaxies.

We see a lot of quasars out to long way in the Universe, but at some point they get much harder to detect, and it’s possible that in the very early Universe they hadn’t switched on yet (remember, the farther away something is the longer it takes the light to reach us, so we see it when the Universe was younger). They’re so bright, too, that they can tell us a lot about conditions in the early Universe as well, which is otherwise extremely hard to find out. So, finding them at greater distances is something astronomers really want to do.

A pair of astronomers published a paper in late 2022 claiming they had found just such a quasar, and it was extremely distant, something like 13 billion light years away. If real, it’s a very big deal.

The object was found by looking at three different sky survey observations; at a given distance the colors of a quasar can reveal its existence — I explain this in an article on The Old Blog. The astronomers then took spectra, which can then reveal a lot more data, including a better distance. The spectrum, according to the discovery paper, confirms that this quasar is at an extreme distance.

The second paper, however, refutes that. They show that the colors seen from the purported quasar are not what they appear. When they examined the data they found that there was a faint object apparently moving across the image, and at the time of the observations it passed very close to a very faint object seen in the WISE infrared data used to discover the quasar.

This, the second team says, is most likely an asteroid in our own solar system, orbiting the Sun between Mars and Jupiter. It was just extraordinarily bad luck to be in the wrong place at the wrong time, and mucked up the observations. The colors of the uncontaminated object don’t match what you’d expect from a very distant quasar.

What about the spectrum the original team took? Well, the second team processed it for themselves* and don’t see the same features the original team did. This claim is harder for me to see, since the second team didn’t publish their spectrum (they published their paper in a journal that has pretty restrictive page limits, so there may not have been room). But I looked at the spectrum in the discovery paper and I have to admit some of the features they claim are from a very distant quasar don’t quite line up as well as they should.

I am not qualified to say whether or not this object is truly a hugely distant quasar, but if I had to bet I’d put a modest amount of money down that the second team is right, and this is a case of extremely unfortunate timing together with a spectrum that’s faint and difficult to process correctly. But I am willing to admit I might lose that bet. It would be nice to get deeper spectra (in other words, a longer exposure time) but that seems unlikely given they used Gemini North, one of the biggest telescopes in the world, to get the first spectra.

Still, it would be nice to know what this object actually is. Just a normal galaxy, or a quasar at lower distance, or what? If this paper is right we know what it isn’t, but not necessarily what it is. Unfortunate.

My point? Science is a process. Sometimes the steps in that process don’t go in the right directions, and you wind up making a wrong conclusion. But the true power of science is that it’s self-correcting; the whole point is to make sure the conclusions you come to are the best ones you can. If better data come along, or a mistake was found, or someone else comes to a different conclusion, that’s all grist for the mill. It all points toward better understanding in the long run.

Who’s right in the Case of the Maybe Really Far Away Quasar? I don’t know for sure. But hey! Like the guy in the video below says: It’s a process.

* Data come off the telescope in a raw format, and need to be cleaned — removing various artifacts, camera biases, and so. We call this “processing” the data, and it can be a delicate series of steps that need to be done with a lot of care, especially when the object is faint.

Et alia

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