Student astronomer finds missing galactic matter | Hacker News Reader

Student astronomer finds missing galactic matter

phys.org

61 pointspseudolus21 comments

A few things:

1. This isn’t a “student astronomer” this is a full on doctoral candidate researcher. Give her the authority she deserves.

2. This isn’t dark matter/energy. This is baryonic matter that is really hard to detect. Nor is it all of the missing matter, it’s just a smaller piece of it, proving that our current estimate of baryonic matter _may_ be inaccurate if we can find more of this stuff than we accounted for.

2. This is a really cool method! We’ve known for a long time that our atmosphere has a significant effect on light coming though it. It’s a great idea to extend that to find a sort of “extra-atmosphere”/gas floating around in space.

I’m excited to sit down and read this through to see their methodology. My only worry right now is: a straight line of gas is a little too perfect? Couldn’t this be more than a line, and possibly a more standard cloud (like other existing structures we know about). I ask because stars are pin points and if you’re getting data telling you it’s a line in the X axis, for example, you’ll also need data in the Y axis to prove that it’s not taller.

Really hope we can extend this to find more undetectable matter and get our equations in check.

So, I'm going to bypass all of the really cool things about the excellent work that this Ph.D. candidates, Ms. Yuanming Wang, has done here and just comment on my amusement that this female Ph.D. candidate and her supervisor, Professor Tara Murphy, were working with Manly Astrophysics (http://manlyastrophysics.org/index.html) on this project. I picture a bunch of buff, bearded, rock-jawed astrophysicists who smoke Marlboro's and wear plaid flannel shirts and cowboy boots while staying up all night in the observatory.

Manly people stopped smoking thirty years ago.

A copy of the paper for anyone who can't read the journal site: https://arxiv.org/pdf/2101.06048.pdf

On reading it, one thing I'm a little stylistically critical of (and this is minor):

They go through all the principles, methodology, findings -- distances, dimensions, (0.1 pc at 4 pc distance), velocity, properties, etc. etc. of this thing.

But I guess in keeping with the tradition of hiding the headline worthy thing that the BBC would want to write about, not once did they just outright clearly say "we believe this is a filament of dark gas in our own galaxy causing this"!

The terms "galaxy" and "interstellar" appear about 4 times total, and only incidentally to describe the history or context. They never simply clarify in plain language that:

-- This is a piece of gas inside our galaxy (versus outside)

-- It's big, and long, floating around between us and other stuff

Maybe writing for an academic audience, you assume everyone understands the obvious and need to make it sound very detailed, but they could sure have done a better job of making it not just sound like a technical addendum paper. Maybe after months of staring at the details, they got the enthusiasm for making a clear simple statement beaten out of them! But there are good examples of paper writing in astronomy that read simply and clearly. Not everything has to sound technical and swamped by the details to be credible.

I might've called it "First detection of a dark matter filamentary cloud in our Galaxy through pulsar scintillation" or something like that.

The article says that 5% of the matter in the universe is normal matter but they can’t detect half of it. How do they know it is 5% normal matter then and not 2.5%?

The baryon to photon number density in the early universe plays a role during big bang nucleosynthesis as well as baryon acoustic oscillations, imprinted on the microwave background. We know that the total energy density must be (close to) the critical density (again from CMB measurements).

I can't really provide more details without doing some reading myself first, though...

CMB means cosmic microwave background right?

Yes.

Would it be possible for all the missing matter to be just unseen baryonic matter? How are we sure that most of this is exotic dark matter?

In the article, it specifically says that the matter she found is, in fact, unseen baryonic matter, and not dark matter. She found a method for detecting it even though it's cold and not emitting any EM waves.

It's also clear meaning light passes through this baryonic matter.

My question is, how do we know that the "dark matter" we assume to be littered all over the universe isn't just clear baryonic matter?

I know that we infer the existence of dark matter through gravity so how do we know that this dark matter isn't just "clear" baryonic matter?

Any astronomers care to share their expertise?

Can’t say I’m surprised. Confirms my opinion that dark matter is just literally that: dark, cold interstellar matter

From the wording of this article it sounds like it’s explicitly talking about missing non-dark matter, which is separate from dark matter. So it wouldn’t ‘confirm’ your opinion.

I'm pretty sure 'dark matter' candidates do include cold baryonic matter, it's just that in large part it's been ruled out due to a lack of observations exactly like the one reported here. The fact that we had not seen it, until now, did not definitely exclude it from the definition of dark matter; it just made it rather unlikely. In the absence of observational evidence, alternative, more exotic theories were developed.

The interesting question is how did this cloud form? One of the reasons, for example, that 'dark matter' can't be cold dead stars is that even if the stars were formed at the dawn of the universe, their remnants would still be warmer than the background temperature of the universe and thus we should be able to see them. Many other 'regular' baryonic sources were ruled out for similar arguments, eg, any process that could have created them would have imparted sufficient energy that we should be able to see it, or it would have been swept up into a star or formed a new star. The article did propose a mechanism, but I wish it went into it in more depth. Figuring out ways to explain the observation could lead to insights we had previously overlooked.

Most scientists also thought it was crazy at first--surely there must be some simpler explanation than just conjuring up a new type of matter. But at this point, the dark matter theory is by far the most popular.

There are a lot of reasons we know that dark matter is (almost certainly) non-baryonic. For one, we know how much baryonic matter there is (based on models of the big bang, etc.) And while no one has seen dark matter in a laboratory, we have observed it indirectly (eg by gravitational lensing).

[1] https://www.nasa.gov/vision/universe/starsgalaxies/dark_matt...

I did a thought experiment once about wormholes, and how gravity would pass through them creating quite a messy curvature of space (potentially dangerously so near a planet or sun).

Don’t we think wormholes would look like gravitational lensing?

Show's again how blind universities are with millions of funding, a stundent has to show them.

Where do you think said student has got training, advice, resources and collaborators from?

Student: literally part of the university.

A PhD student, working with other researchers on the cutting edge of their field.

Had the university not been funded, the PhD student and the team who came up with the idea may not have attended said university and the discovery would not have been made yet.

In addition, universities often return back much more than they are given in funding, for example, universities in the ' League of European Research Universities' such as the University of Copenhagen return five fold the investment [1].

[1] https://about.ku.dk/facts-figures/value-for-society/

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