astro123

7 ms·

1.
by astro123 5y ago
Measurements of pretty much any time in the universe can test predictions made by models of the early universe. One of the main reasons we think there was inflation is from late time (near today) observations of matter density (see https:&
2.
by astro123 5y ago
Inflation happened during the first tiniest fractions of a second post big bang. No telescope is going to make direct observations of the inflationary period so I'm not sure what you mean by this.
3.
by astro123 5y ago
I worked with someone (this is in astronomy) who said that papers in nature were the most likely to be wrong. They are in nature because they have a dramatic (new/unexpected) result. One good reason for a new/unexpected result is
4.
by astro123 5y ago
Small stars live a very long time. A star of the mass of our sun has a lifespan of ~10 billion years which gets you almost back to the beginning of the universe (~13 billion). This star is smaller (0.8 solar masses), so it can live even lon
5.
by astro123 5y ago
That's a weird distinction to try to make. Metal does mean the elements, not the spectral lines. The presence of those elements is usually inferred from the spectral lines, but if another method was used we would still say "metal
6.
by astro123 6y ago
> It seems significant that the lens galaxy has little dark matter I don't see that in the article? They centered on galaxy clusters which contain huge amounts of dark matter. DM is needed to account for lensing. There isn't en
7.
by astro123 6y ago
I think it was taken at a particular time. If it were the closest, venus would be closer than the sun. Skimming the paper it looks like it was the positions in Aug 2003
8.
by astro123 6y ago
The early universe's expansion was not accelerating, as the early universe was not dominated by dark energy. I don't know off the top of my head exactly when that changed, but z=0.76 seems about right. So I'm pretty sure that
9.
by astro123 6y ago
There's no strong lensing there. If the background galaxies were lensed enough to have multiple images they would also be incredibly distorted. But that does look like a small group/cluster. Edit: Here is an example of strong lens
10.
by astro123 6y ago
Eek! I guess I'm more OK with this now...
11.
by astro123 6y ago
The best suggestion I have is https://astrobites.org/ These are paper summaries, written by people in the field, where you are probably the target audience. I don't read it myself, but give it a go!
12.
by astro123 6y ago
Yup, by fringe I meant "On the edge of what reasonable people are working on". But maybe it's not a great term if people misunderstand.
13.
by astro123 6y ago
That's a fair point. I love reading computer hardware rumours, most of which are probably total garbage (and probably obviously so to anyone in the field). And in this case, whether the general public thinks the universe in MOND or LCD
14.
by astro123 6y ago
No-one is making an argument by authority. Here is a nice popular article that outlines some of the issues with MOND https://www.forbes.com/sites/startswithabang/2018/03/06/only... I just think that
15.
by astro123 6y ago
The astrophysics journal (ApJ) is a really good journal. A majority of good astronomy papers are published in ApJ or in MNRAS. Big things go in Nature/Science + then there are other smaller journals. (At least this is what I tend to fi
16.
by astro123 6y ago
I only skimmed the paper past the abstract, but for what it is worth. The MOND favouring group is a fringe of the cosmology community. The vast majority feel that there is enough evidence to rule it out. I mostly mention this because I don&
17.
by astro123 6y ago
I'm not suggesting that at all! I'm just saying it took 30 odd years to take off/break out of the nuclear physics world. Though rereading my first comment that wasn't entirely clear...
18.
by astro123 6y ago
Kringing is the same thing as gaussian process regression, and astronomers use GPs a fair bit. I'm not sure whether they are used more widely. My favourite forgotten/isolated statistical method is MCMC. These were first used by nu
19.
by astro123 6y ago
I didn't know about that, that's really cool! Thanks for letting me know.
20.
by astro123 6y ago
I don't think that is right, though I'm not a GW expert so please tell me if I'm wrong. I think they know the difference just by looking at the mass. i.e. we think it is hard to form black holes smaller than ~3.3ish solar mas
21.
by astro123 6y ago
That's an interesting question. I've never thought about it or seen that taken into account (its not something we fit to when constraining cosmology) I just looked around and LIGO has constrained Omega_GW < 1e-7 (they find no e
22.
by astro123 6y ago
I highly recommend these books by Alan Hirshfeld [1][2]. The first is about the discovery of parallax, and the instrument that was used to do this in 1838 was built by Fraunhofer. The precision of the instrument required to do this is incre
23.
by astro123 6y ago
We have! A constraint on dark matter is that it needs to be around at very early times. Before the time of the CMB (400 000 years after the Big Bang). If there wasn't dark matter at this time, the under/overdensities of baryons al
24.
by astro123 6y ago
While yes, better launch capability == cheaper to put telescopes in orbit == good for astronomy, its not that simple. Interferometry is HARD. The Keck telescopes which sit 100m apart on the surface of the earth were designed to be used as a
25.
by astro123 6y ago
The argument is actually really really simple. If it started from within the solar system, it would not (barring some three body interaction) have enough energy to escape. But, we know from observations that it does have enough kinetic ener
26.
by astro123 6y ago
I read a lot of astronomy journalism that I think is absolutely awful (one of the main reasons I made this account was to point out garbage articles/comments). I actually think that this is pretty good. It mostly follows the paper (her
27.
by astro123 7y ago
Famously, Hubble's 1931 paper that detected the expansion of the universe found H0 ~ 500 km/s/Mpc (fig 5 in [1]). The distances that he was using were way off... Through most of the late 1900s the uncertainty was between 50 a
28.
by astro123 7y ago
> That sounds a little like parameter fitting. You're exactly right. We have a model (Lambda CDM + GR + a few other details). We have ways to generate descriptions of how the universe would look given certain parameters (H0=70, Omeg
29.
by astro123 7y ago
> Is it simplistic to conclude that it's this? > Dark energy, the model presumes, takes the form of a cosmological constant Λ ... Yup quite possibly, and there are people investigating it! The extended model is "Time depende
30.
by astro123 7y ago
I'm 99% sure this isn't true. Can you point to a single paper that mentions it? Edit: actually I'm 100% sure this isn't true. See for example the all sky map from planck ( http://www.bbc.co.uk/news/sp

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