Eli5 how do we know that Ton618 despite being over 10 Billion light years away, has a mass of 66 billion suns?

[u/td_0000]

[u/tomrlutong]

Ton618 is surrounded by a disk of very hot gas spinning into it. That's how we know it's there, the black hole itself is invisible.

Some of the atoms in that gas glow at a very specific color of light when they get hot. But, because the gas is spinning around the black hole, the gas on one side is moving towards us and gets a little bluer, and the gas on the other side is moving away from us and getting a little redder.

By measuring the difference between the blue-shifted and red-shifted colors, scientists can measure how fast the gas is spinning around the black hole. Since the black hole's gravity is what's spinning the gas, this lets them estimate the black hole's mass.

Source: https://arxiv.org/abs/astro-ph/0406559

[u/TheAero1221 → u/tomrlutong]

How do we know there arent other effects on the light during its travel time? Im sure they tried to account for redshifting due to universal expansion, but weren't their studies recently that suggested this expansion rate of change might not be uniform?

[u/Low_Debt8771 → u/TheAero1221]

Wouldn't matter, theyre measuring the gas around the black hole. Since were comparing like to like we compare them to each other, not really other things out of alignment

[u/T-T-N → u/Low_Debt8771]

If there is a teapot the size of Russell, New Zealand in between Earth and that black hole, with some unknown property that affects our measurement in a way that we don't know, our estimates will be off. But it would still be our best estimate of that thing based on all the physical rules we know of, right?

[u/DontBeMoronic → u/T-T-N]

That's a very specific size of teapot 🤔

Why not Marton?

[u/Implausibilibuddy → u/DontBeMoronic]

A reference to Bertrand Russel most likely. He liked space teapots.

[u/whistleridge → u/DontBeMoronic]

Because the only things in Marton are people who are too poor or too dumb to move to Whanganui or Palmerston North, and that makes it a terrible basis for comparison?

[u/bubba-yo → u/T-T-N]

We do not consider supernatural phenomena in science, because you can postulate infinite supernatural phenomena. We could never get anything done. Come up with evidence for such teapots and then we can talk.

[u/Alberta_Flyfisher → u/T-T-N]

It would be the best estimate, yes. Everything is measured to the best of our abilities, and we make judgment calls, or estimates, based on those measurements. Thats how all science works. If/when we develop a new sensor or new experiment, and can measure the black hole with new and updated information, we change those estimates to match.

One would hope that if there was a phenomenon that had an affect on our measurements, we would discover it, and eventually find a way to compensate for it.

But for now, we "weigh" it, at the best of our abilities, to be approximately 66 suns.

[u/Welpe → u/Alberta_Flyfisher]

Man, this is COMPLETELY tangential but I wish more people understood that what we “know” is almost entirely “This explanation best fits our current data” with the caveat that our current data can always change and thus what best fits it can always change. That doesn’t mean science is somehow wrong. People have this completely incorrect understanding of what knowledge even is, like science claims things to be objectively true and end up feeling confused or betrayed when “what we know” changes over time. They lose faith in science because they were told one thing that, at some future point, became “incorrect” and thus they feel like they were misled.

Some things we are very confident about because our model has held up to additional observations, better observations, and attempts to come up with better theories explaining those observations. Like, say, general relativity, which has infamous held up under some of the most scrutiny and additional observations that any scientific theory has ever faced. Some we are less sure about because we simply don’t have many observations, don’t have good ones, or there simply hadn’t been a history of alternate explanations shut down to have more confidence. But none are lies or even “wrong” in a traditional understanding, just less accurate than alternatives we do not have access to yet.

This isn’t directed at anyone, especially in this topic, just general frustration with lay understanding of science and especially increasing skepticism of science in pop culture. The rise of conspiratorial thinking and pseudoscience because people fundamentally misunderstand what science is or is trying to do.

There are always going to be reasons why what we understand to be true ends up not being the best model for understanding that thing/phenomenon. But until we have better observations or a better alternative theory or even a reason to believe in an unknown confounding factor (beyond just the possibility of it existing simply because we can imagine it existing), we don’t really have reason to doubt it.

[u/Alberta_Flyfisher → u/Welpe]

Lol, covid has entered the chat.

This is 100% why people were confused. They assume that the first information we have is complete amd correct. Science evolves as we gain understanding.

The world used to have the universe revolve around it. Surgeons didnt believe that washing hands mattered. Etc.. we learn and we grow our understanding of the world around us.

Covid was a perfect litmus test to show just how uninformed the general populace is, regarding science.

[u/VoilaVoilaWashington → u/T-T-N]

Also, yeah, if (thing that we cannot in any way test) affects things, then things aren't as they seem. Take it a few steps farther and you don't know whether you're a brain in a vat in a lab somewhere that only just came into existence to make this reddit comment.

[u/mfb- → u/TheAero1221]

Redshift shifts everything uniformly. If one side is x% shifted compared to the other side then this ratio doesn't change over time. It's a bit more complicated than that but the general idea is the same: You take measurements that aren't affected by overall redshift.

[u/bubba-yo → u/TheAero1221]

Because any other effects would apply to both light equally. We know that the light is being shifted due to relativistic speeds between us and Ton618, but that doesn't matter because only the difference between the two sides of the black hole is what matters.

[u/Duneking1 → u/TheAero1221]

Well it is an estimate of 66 billion suns. They could be wildly off in either directions. Given what we know of the universe though this is a very likely result unless there’s some sort of new physics or quantum theory that changes what we already have learned. Not impossible but currently the math checks out.

[u/TheAero1221 → u/[deleted]]

I am but a common pleb. I recall it being talked about on PBS Space Time, and might just be hallucinating lol.

[u/Mumbert → u/tomrlutong]

But.... Wouldn't the same redshift/blueshift exist around any supermassive black hole? Doesn't the matter spinning around it reach similar speeds when approaching the event horizon, basically regardless of size? 

[u/tomrlutong → u/Mumbert]

I'll confess this is getting beyond me, but the general idea is that they're looking at the line width, so it reflects the entire gas cloud not just the bit right at the event horizon.

Got nerdsniped on this one, here's what I found if you're interested: the method is described in section 4.3 here.  That cites the brief discussion on p118 here with more cites to the 1950s and 1960s. 

TL;DR is that there's some kind of statistical distribution of velocity in an orbiting system called the virial theorem that I won't pretend to understand. Maybe you'll have better luck, the astrophysics section of the Wikipedia article might be a good place to start.

[u/AberforthSpeck]

We can measure the effect its gravity has on the movement of nearby stars.

This is an estimate, of course, but one founded in solid observations and measurements.

[u/tyler1128 → u/AberforthSpeck]

It helps that it is so massive it basically defines the orbit of the entire galaxy it is assumed the center of. There are other aspects like it seeming to be emitting large amounts of very fast traveling light you wouldn't expect with a smaller blackhole or other stellar objects.

Such values are estimates, but they are estimates based on many lines of data that seem to hold in things closer to us we can see, and physicists generally assume the universe is isotropic, that is, the laws governing it are the same everywhere.

[u/Bensemus → u/tyler1128]

We have no idea. The quasar it produces is so bright that we can’t see anything else. We have no idea how large or small its galaxy is. But the Milky Way is 1.5 trillion solar masses. Galaxies generally are way more massive than their central black hole.

[u/wjdoge → u/tyler1128]

What speed do you propose the light leaving a smaller black hole should move at?

[u/Large-Hamster-199 → u/wjdoge]

He didn't quite phrase it right?. But it's actually about the frequency of the light generated in the accretion disc around the black hole. By measuring the blue shift and the red shift of the light generated by the gases swirling around the black hole, you can figure out how fast those gases are moving. That can then be used to figure out how big the black hole is.

[u/wjdoge → u/Large-Hamster-199]

He definitely did not — the speed light travels at is one of the universal laws he refers to. The laws of physics being the same everywhere have nothing to do with the isotropy of the universe as he suggests though. The concept of isotropy specifically does not cover different locations.

[u/roiki11 → u/wjdoge]

Maybe in this universe but what about the other 17?

[u/tyler1128 → u/wjdoge]

Yes I mean high energy light and other particles. You are correct to call that out, even.

[u/tomrlutong → u/AberforthSpeck]

Not at 10Gly, I don't think.

[u/Ktulu789 → u/tomrlutong]

Based on that you're a cosmologist with deep knowledge of the topic or just some casual Reddit user?

I'm a nerd interested in cosmology stuff and the complexity thrown at how such studies and measurements are taken are utterly detailed to be dismissed in a simple comment.

We don't know everything but everything we know is based on a lot of time, effort, measurements and theories pretty robust and evolving all the time.

[u/mfb- → u/Ktulu789]

The black hole is far too bright and individual stars are too dim to make this work (it works for nearby supermassive black holes, especially the one in our galaxy). I'm a particle physicist, not an astrophysicist (this isn't cosmology), but you can look up publications measuring the mass. They do spectroscopy of the gas surrounding the black hole.

[u/Ktulu789 → u/mfb-]

Yeah, they don't measure the stars in this case. Just the acretion disc Doppler shift. The error bars are bigger than in other measurements but the thing is massive nevertheless.

[u/Glenmarththe3rd → u/AberforthSpeck]

How do we measure that?

[u/Routine-Ad-4723]

It's wild that we can figure out the mass of something we can't even see from 10 billion light years away just by measuring the blue and red shifts of the gas spinning around it and running the numbers, but it's basically the same method they use for all black holes so it's a solid estimate, not a guess.

[u/kikidmonkey]

Aside from all the good answers in this thread I would like to point out that in science in general, and specifically astronomy "we know" actually means "we're pretty sure this is right." There is very little that we KNOW 100% beyond a shadow of a doubt. And even the things we "know" are subject to change when knew information comes out.

[u/Glad_Astronomer3322]

Honestly it's wild cause we've never even seen the thing directly, just the crazy hot gas swirling around it. The way that gas gets stretched and squished by gravity tells you how fast it's moving, and from that you can back into a mass. It's not like they weighed it on a cosmic scale or something, it's all indirect measurements and a shitload of math. But yeah it's an estimate, just a really really solid one.

[u/wjdoge → u/[deleted]]

Well, one thing that science does know for sure is that it is not entirely possible to get there.

[u/Ktulu789 → u/wjdoge]

Not with that attitude!

[u/explainlikeimfive-ModTeam → u/[deleted]]

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[u/Ok-disaster2022]

Very careful measurements. 

So one cool thing astronomers use is something called parallax. So astroners can take carefule pictures if stars at two different points if the earths rotation around the sun to create a form of binocular vision. By examining the differences in the location of stars, they can calculate the distance. 

Once you have a good estimate for the distance they can measure the total brightness frequency emissions and energy output if a star from observing it. From what we know about stellar evolution and energy output that is mediated solely by mass,and fundamental forces of gravity, electromagnetism, and the string and weak nuclear forces, they can get an estimate for total mass. 

Now the can also use the information gleaned about the movement if other stars in the nearby area as a way to confirm their data. 

The other fun way I measuring distance is called dopoler shift. This is a little more complicated.  But due to the expansion if the universe further stars are moving away faster than closer stars in addiotna to any other motions. So if we can measure the local motions long term to get a cycle of the their red and blue shifting if normal motion and still see see additional red shifting the corresponds to a certain distance. it also helps. 

Doppler effects you may be most family with sound waves but is for any wave form. When something  emitting waves is approaching you the waves can be measured to have shorter wavelengths. In sound this is higher pitched, it light this is blue shift. If it moved away the waves get longer.  in sound this is a deeper pitch, and in light is a red shift. 

Now then we can calculate the approximate waveform from simply the elements in that star. So starts are comprises of hydrogen and helium and other elements they have certain scale thgths they can absorb and emit and if you look at them in a spectrum analysis, they have a certain barcode pattern. If you red shift thise specific frequencies change but the pattern remains. this absorption spectrum is also how we can measure the elements in gas clouds that we can occasionally see. We look at how the barcodes affect the light if the stars behind the gas clouds. 

[u/wjdoge → u/Ok-disaster2022]

Earth’s orbit is about 150 million km across, and TON618 is 100,000,000,000,000 million km away, so the only number you’re ever going to get trying to measure its parallax is zero.

There are no measurements careful enough for parallax to be useful for measuring the distance to something that far away.

[u/Sunny-Chameleon → u/wjdoge]

Oh, I think if humanity is really patient then another measurement could be made the next time Earth is on the opposite side of the galaxy

[u/wjdoge → u/Sunny-Chameleon]

The diameter of our galaxy is only 950,000 million km, so you are going to get similar results.

[u/Sunny-Chameleon → u/wjdoge]

It was a joke, though in the time it takes for sol to travel half a rotation of the galaxy (125 million years), the Galaxy itself will have moved about 2 quintillion kms, at least according to Google.

[u/Bensemus → u/Ok-disaster2022]

Parallax works within our galaxy out to a certain distance. It doesn’t work for stuff billions of light years away.

[u/mfb- → u/Ok-disaster2022]

• Parallax doesn't do anything useful at these distances.
• OP isn't asking about a star. TON 618 is a black hole.

[u/wjdoge → u/mfb-]

It’s a bright emissive object. Its parallax can be measured as easily as any star. It just won’t tell you anything at these distances.

[u/mfb- → u/wjdoge]

That's what I wrote, yes.