Astronomers just discovered the farthest object in the known universe | Hacker News Reader

Astronomers just discovered the farthest object in the known universe

livescience.com

82 pointswglb62 comments

Key sections:

"The researchers discovered HD1 in data collected over 1,200 hours of observation time using the Subaru Telescope, the VISTA Telescope, the U.K. Infrared Telescope and the Spitzer Space Telescope. They were particularly looking at redshift, a phenomenon in which light waves stretch out or become redder as an object moves away from the observer. In this case, the redshift suggested HD1 was extremely distant.

The researchers found that the red wavelengths were the equivalent to a galaxy located 13.5 billion light-years away.

HD1 also seems to be growing at a feverish rate — about 100 stars each year, or at least 10 times the rate predicted for starburst galaxies that are known to produce stars at an extraordinarily high pace.

These stars were also more massive, brighter (in ultraviolet wavelengths) and hotter than younger stars, the researchers found.

As such, HD1 could be home to the universe's very first stars, called Population III stars; if that identity is verified, this would be the first observation of this type of star, the researchers said. There's also the possibility that HD1 is a supermassive black hole with a mass of about 100 million times that of the sun."

Also a paper on it: https://arxiv.org/abs/2201.00823

I can't wait for JWST to look over there!

Paper sez: z ∼ 13

How do they count the number of new stars?

I mean, it's way too far away to see individual stars.

no, due to gravitational lensing, you can see stars. For a straightforward break down, see Dr Becky, https://www.youtube.com/watch?v=VChgsXbIgdw

Oh grief, I've tried getting into her channel a few times because the content and analysis is fantastic, but the 'effervescent' delivery style is excruciating.

What’s your email address? I’ll send you my toenail moon images.

This galaxy is not being gravitationally lensed though.

We have models for how much light a star of a given mass, age, chemical composition etc. puts out as a function of wavelength. We can then take mixtures of stars and predict the total light output of a stellar population in different bandpasses. So from observations of a galaxy in these different bandpasses, we can use these models to determine things like the age of the stars in the galaxy—from how old the stars in the best fit stellar population are—as well as the mass (or number) of stars—from how many are needed to match the observed brightness of the galaxy.

That makes sense. Thanks!

Layperson's question: The article talks about "a possible galaxy that exists some 13.5 billion light-years from Earth". But isn't that just the light traveling distance, and the object should actually be much further away due to the expansion of the universe?

Well spotted yes, by now that object will be about 45 bn ly away. The light reaching us from it has only traversed 13.5 bn ly though.

Define "now"

https://en.m.wikipedia.org/wiki/Relativity_of_simultaneity

While that’s a problem in theory, to moderate accuracy it’s not a practical issue. Most objects in the universe are roughly at rest relative to the cosmic background radiation (in other words they don’t see it as Doppler shifted in any particular direction), so we can use that as a common frame of reference. When we’re talking about ballpark integer billions of years, or even to a few decimal places, that’s easily good enough.

Accuracy? "Now" is an inaccurate (nonsensical, actually) concept except in extremely local conditions.

It's perfectly sensible given a common frame of reference, which we have thanks to the CMB. Frames of reference aren't local. We have clocks and can measure time on them just fine, and 'now' is just a time on a clock.

What are you basing the 45 bn ly on? A redshift of z~13 should correspond to a comoving distance of about 33 bn ly, whereas 45 bn ly would correspond to z~600.

You may be right, I've just seen ~45 bn ly given as the radius of the observable universe accounting for expansion. The discrepancy could be due to changes in the rate of expansion over time, as it hasn't been constant.

45.5 bn ly is the approximate comoving distance of the surface of last scattering (the source of the microwave background and the point where the universe becomes opaque). This is the boundary of the universe observable via electromagnetic radiation.

“Light-years” literally is light-traveling distance, though. :)

Speaking as someone who used to teach introductory cosmology at a good university ... your question is not a layperson's question! (That's a compliment, BTW.)

What is the expansion of the universe? Or should I first ask, is there a center?

The best analogy I've ever gotten is to think of an expanding balloon. Where on the surface of the balloon would you call the center? And if you imagine yourself standing on the surface while it expands, you will be still while all other points of the surface move away from you.

It's far from a perfect analogy, but probably the best way to visualize in human terms.

What is the expansion of the universe?

The distance between galaxies (that aren't gravitationally bound to each other) increases over time.

Or should I first ask, is there a center?

Probably not. If you inflate a balloon, any point on its surface will move away from any other point on the surface. And yet, no surface point can claim to be central.

Note that in the balloon example, there is of course a central point within the volume of the balloon. This is where the analogy breaks down: In case of the universe, we do not assume the existence of an ambient higher-dimensional space.

A perfect geometric surface of a sphere that is expanding has no center, but a balloon has a center. That's obviously the nozzle. The analogy breaks down in both places.

But who knows? Maybe the analogy is correct. I don't think we can say. In fact I would even wager that a "center" is more likely... because can you even imagine a real world analogy where something expanding has no center?

If you can't then there probably is some sort of center.

There's nothing special about the nozzle; it's just another point. The nozzle isn't the center. But if you can't get past that, imagine a balloon without a nozzle, with a canister of compressed gas inside, and the compressed gas is leaking out of the canister.

I mentioned a perfect geometric sphere that is expanding has no center on that surface.

I also stated that no real world analog of a perfect expanding sphere exists. Because we can't imagine an analog it's much more likely that the universe DOES have a center similar to the nozzle.

Try to imagine a real world analog to the expanding geometric sphere without a point of discontinuity. You can't. And because you can't maybe it doesn't exist. Maybe it does. But not being able to imagine a real world analog is slight evidence that there there is a center.

As soon as you can imagine and reason about infinity, you might be able to reason about our universe. “Center” makes sense for most bounded things but might be completely meaningless in an unbounded universe.

Example: the number line. You might be tempted to say 0 is at the center but… there are an infinite number of things on either side of any number you choose.

Does that mean nothing is the center of the number line?

Or everywhere is the center of the number line. Some people argue 0 is the center based on symmetry. My original point is that it is non-trivial to reason about infinite spaces. Since we do not know if we live in a bounded space or not, we can’t assume there is one center. Furthermore, even if we do live in a bounded space, there are different ways of measuring center. Eg: center of mass vs geometric center of a volume. Knowing both and comparing them would be pretty interesting!

0 is the center of an infinite number line.

Additionally nobody knows if the universe is infinite.

From an observer's point of view all the oldest gallaxies are distributed in the "surface" of a sphere of radius 13.5BLY, that surface IS the center of the Big Bang, the past, and the center of "now" is the point of the observer. Isn't this mind-warping?

Specifically, Wisconsin is the center. ;-)

The way to reconcile this paradox is that every person experiences the same thing, wherever they are located in the universe, but each person sees a different surface.

Best explanation of "the center of the big bang is the past" I've seen, bravo.

To add my dumb question: since the universe expands faster than light, how is this considered a very far object and not just that we're looking at something in the past? Is this confusion of mine between distance and time what physicists mean by space-time?

If that's the case, why isn't the article titled "astronomers just discovered the oldest object in the known universe"?

Distances of this sort of thing are not measured directly - what's measured is its red shift, which tells us both how distant it is (very) and how old it is (very). That inference is indirect and depends on the model of cosmology, but the relevant bit of cosmology is relatively uncontentious.

(But if it really was only 13.5 billion light-years from Earth then you'd be right. In fact it's much further away than that.)

It sound odd, but that depends on what you mean by "now"[1]. If you mean, where would the galaxy be if I traveled there at the speed of light, you would actually travel less distance due to Length Contraction [2].

[1] https://en.wikipedia.org/wiki/Relativity_of_simultaneity [2] https://en.wikipedia.org/wiki/Length_contraction

It sounds odd to interpret it like that and not as usually a layperson ignoring relativity&physical limitations would mean it?

"Now" as in if I could just teleport there!

Is there a physical limit to the resolution we can get from such absurdly large distances? And if so - is there an equation?

I vaguely recall that image resolution is a function of total photons inbound, distance to the object being observed, and effective sensor size.

The photon density (assuming the source is not a point source) varies over the distance to the observed object, which will place a theoretical limit on resolution.

The other half is sensor size, ie, can we catch enough photons to make sense of what's emitting/reflecting them?

I haven't touched optics in a long time, though.

It's proportional to the aperture diameter and inversely proportional to the wavelength. That's why they needed telescopes that spanned the globe for that image of a black hole. More photons does get you shorter exposure times (and therefore better temporal resolution, fair enough).

JWST by the way is able to resolve at this theoretical limit, which is just wild.

The theoretical limit for resolution comes from diffraction. It is a function of the wavelength of light being observed, and the size of the telescope.

This is measured by the Rayleigh criterion

For a telescope with a circular apeture, the resolution is given by aproximatly R ~ 1.22 λ/D where:

* λ is the wavelength * D is the diameter * 1.22 is the first zero of the intensity function for the Airy Disk

A lot of the work on distant galaxies is not being done with gravitational lensing. The idea is that you use massive objects in the foreground, like galaxy clusters, to focus light from the background. Depending on orientation, we can get magnifications of more than 10,000. There was a recent press release of such an example. So in principle, our telescopes combined with gravitational lenses can resolve almost all of the relevant detail we would want of a galaxy if the orientation is correct. It rarely is of course but there are a few examples so such strong lenses.

Share this with your kids! Just showed the timeline picture to family to explain to them when we see something distant it is light crossing a chasm. As someone who was really into astronomy as a kid, field by interest from father and grandfather, this announcement is really exciting.

Would it be more accurate to say 'oldest' since it's not there as we're seeing it now?

I suppose it's all the same in space-time. But what we study about it is more in relation to the time of the light rather than the place, so 'oldest' has a more relevant connotation.

We have also seen very old objects closer by.

The Methuselah star is estimated to be 13.7 billion years, in fact by some estimates older than the universe (which is clearly somewhat problematic).

It is a mere 190 light years away.

So the calculated age of the star is wrong (ie, our observations are correct and our underlying theories about how stars age is wrong), OR our observations are incorrect.

The former is a far more interesting case, IMO.

One thing that is unusual about the star relative to our regular experience is how little “metals” it contains (in astrophysics metals are any elements heavier than helium).

Metals heavier than iron are only created in supernovae, lighter metals still only get created in stars. Either way, if it was created a few 1e8 years after Big Bang, there weren’t many of those going around.

Now, most of our models for stellar evolution are calibrated to stars we see, which have plenty of metals in them. Whereas this one doesn’t so our models could be off.

This is a different sense of 'old' as in "What is its age?" That's a vague question unless there's no change. e.g. Ship of Theseus or stepping in the same river twice.

The image (information) of Methuselah we see is 190 years old. Saying farthest vs oldest disambiguates.

Unrelated observation: everything travels through spacetime at the speed of light. It's not a speed limit, it's the only speed. If you're not travelling through space then you're travelling through a purely time-line at c. Really makes one wonder how much time we casually waste.

If it’s only 500 million years from the Big Bang, is it possible we could capture a picture of the Big Bang?

We cannot because light could not travel through the early universe. That took half a million years or so and the light from then has now redshifted into microwaves and has been imaged in great detail.

So if we saw something older than this thing (roughly), would that fundamentally disprove the Big Bang?

My understanding of the current state of the science is that there are many theories of the early state of the universe and early star formation but not a lot of definitive proof for any of it. However, the Big Bang is quite sound and as a rough theory has been well established since Hubble (the astronomer, not the namesake telescope) started measuring red shifts of galaxies. They actually have found stars that appear older than the universe, but the it's mostly believed that that's a problem with estimates of star age. All that said, there is plenty of research to be done from all angles.

The closest we have from that is the cosmic microwave background I believe.

Here's the picture https://www.esa.int/var/esa/storage/images/esa_multimedia/im...

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