perpetually_stargazing

hello! welcome to perpetually-stargazing! I'm perp, and I'm currently an undergrad university student studying physics with a minor in CS.

life's tough out here but I'm getting through my degree a quarter at a time, and one of my profs suggested that we microblog about physics topics we like in preparation for future applications and events.

turns out, I really like this idea, sooooo

I'll be microblogging about things I see across the web, probably most prominently from Scientific American or whatever I come across in Arxiv.

if you're reading this blog, thanks for hopping along for the ride! I might occasionally post things about how my degree is going, and I'll try to filter these with "perpetually rambling" or "perp does physics" so you can avoid these if you're just here for the physics :D

I should warn, I tend to drift towards astronomy and particle physics, though I will try to post about topics not just related to these. stargazing is in the name though, so you should expect mostly astrophysics + adjacent posts.

I want to talk about the standard model of cosmology. Currently, we have mapped out the universe to this rough timeline:

Now, this timeline isn't entirely correct. We can only see up to the "First Light" portion of the timeline, which is something called the Cosmic Microwave Background (CMB). The CMB is super super cool! (it's my research and that may or may not make me biased 🙂)

The CMB is the oldest era of the universe we can physically observe. We predict that after the Big Bang, the universe was a very tightly bound, hot, dense particle soup. (I want soup of the mushroom variety ngl)

So dense, in fact, that light could not escape! When things cool down, photons are able to escape (photons are what light is made of). Things cool down sufficiently, and the first photons escape, and we get the above map. This is the CMB.

The history of the CMB is actually really interesting. I believe it was first found because some folks trying to do radio astronomy kept getting this irreducible noise in their measurements, which wasn't caused by the instrument. At the time, the CMB was only a theory that would have supported the Big Bang, so this unremovable noise was kind of a hopeful indication that the Big Bang model was correct.

Folks at Princeton basically confirmed this because they were building something to specifically measure the CMB at the same time, so I think the two groups ended up splitting the Nobel Prize, lol.

Anyway, I think the CMB is really beautiful because you can model it with 6 parameters! Currently, the universe is described with the "Lambda CDM" model, (CDM = cold dark matter), which describes a universe governed by dark energy and dark matter. With parameters describing the baryon matter (like, atoms that we interact with on the daily) density, radiation density, Lambda density (dark energy), and the curvature of space (currently presumed to be nearly flat), a Hubble constant (one of the biggest tensions right now and warrants its own post), and a bunch more (I'm still learning them), we can effectively build a model for the entire universe.

Which is so freaking neat. This is probably my main motivation for studying this stuff. Anyway, CMB measurements have really improved over the years:

And they're about to get a loooot more precise. There are a few observatories, Simons Observatory (SO), South Pole Telescope (SPT), Atacama Cosmology Telescope (ACT, now decommissioned), and CCAT, which are about to make CMB observations so much more precise.

I will get into precisely why this is important in a later post, but there is some ambiguity within the universe timeline (like, what happened between the Big Bang and the CMB? we have theories, but we aren't entirely sure), and tensions (such as the Hubble tension) that need precise data to further advancements in.

But, the special thing about the CMB is that it exists at mostly a uniform temperature. (2.7 K, approximately!) There are very very small fluctuations, like 10^-9 K, that we can map out with these new observatories. Understanding these small, small fluctuations can really inform us what happened immediately after the Big Bang, and I'm personally very excited about this.

OK, now I need to get back to my research so that I can help this goal happen, haha. But I think I'm gonna make this a series because cosmology is really freaking cool and there's a lot of open questions I have that I think I can better formulate and state the motivation for in these types of posts.

there's this thing called "multimessenger astronomy," where basically, instead of looking at things in the visible light spectrum all the time, we have multiple ways of observing an event in space. you guys have probably all seen the first-ever image of the event horizon of a black hole (M87) in 2019:

but, direct imaging is HARD. real hard. especially for objects like black holes, where light is bent so much that it cannot escape the spacetime curvature. however, M87's black hole is spinning! meaning, gravitational waves (like, ripples in really tightly stretched fabric), are traveling through spacetime and eventually reaching us.

you cannot see gravitational waves in visible light, but if you have a laser interferometer, like, say.... LIGO (Laser Interferometer Gravitational-Wave Observatory) from Caltech and MIT, then you can detect these gravitational waves and confirm the existence of this black hole. (in fact, this is how we confirmed that black hole mergers really were a thing!)

now, that was kind of a side tangent, so back to what I wanted to talk about: if Betelgeuse, the closest red supergiant to Earth, were to go supernova tomorrow, we would be able to see it in visible light eventually. we would be able to detect the gravitational waves from the event a few hours before the light reaches us, and so folks at LIGO could inform telescope operators all around the world that there would be a supernova for us to see soon.

however, even faster than this is if we detect neutrinos from a supernova. this is the cool part!! neutrinos are small and weakly interacting, so they are very efficient in taking excess energy out of a supernova and zooming away with it. since supernovae are HIGHLY energetic events, you will have SO MANY (like, on the order of 10^58) neutrinos escaping the explosion.

there are a few neutrino detectors that are active right now, and many in the making. one of the most prominent ones is IceCube. IceCube definitely warrants its own post, so I won't go into it just now, but it is what it sounds like.

literally :)

these energetic neutrinos would reach us around the same time the gravitational waves would, but it wouldn't be an event that is easily confused with another thing. few events in space create so many neutrinos, and spikes in the amount of neutrinos detected, along with confirmation from LIGO, would inform you, with nearly dead certainty, that you would be about to see a supernova with a telescope.

which is sooo freaking cool! we don't understand a lot about neutrinos yet (especially not me), because they are so small and weakly interacting. however, the fact that they can inform us greatly about events happening in the universe makes them very valuable mailmen for cosmic events.

NEUTRINOS! I'm not gonna get into them with much detail because I am not a particle physicist and I don't know jack. however, what I do know is that they are weakly interacting particles that are suuuuper tiny. I guess what is counterintuitive is that light particles (photons) have 0 mass, and still interact heavily with electromagnetic fields and such. neutrinos, on the other hand, are able to pass through space barely interacting with any type of radiation or field.

this means they are very VERY good at taking away energy from things that don't want it! one such example is the big bright blinding sun. which I feel like I haven't seen in a week...

the Sun is a big ball of hydrogen gas that is constantly fusing into helium gas, and SOMETIMES. very rarely. the helium gas can fuse into carbon, nitrogen, or oxygen. both of these fusion processes release neutrinos, because neutrinos can remove the energy from the Sun more efficiently than photons can. (light from the Sun actually can take thousands of years to reach us! the light that is 8 minutes away is the light that successfully got out of the Sun, so think of it as a backlog, I guess)

since neutrinos are tiny and ignore everything, they whiz right through the Sun's layers and outward into space. sometimes, we can detect them! (this process is huge and interesting and warrants another post and I need to study for my final tomorrow so I'll write about the experimental stuff later), but in 2020, the Borexino collaboration in Gran Sasso, Italy, found pretty solid evidence that they detected a neutrino with the correct amount of energy to be a result of a CNO (carbon, nitrogen, oxygen) fusion cycle, from our Sun.

detecting neutrinos is already hard, and very rare. the fact that we have found one relating to the CNO cycle, which is NOT the dominant fusion cycle in the Sun, is insanely freaking cool and lucky! anyway, I was reading a paper about this and just thought it was fun, this post is filled with unfinished thoughts and half-ramblings, but there's your occasional dose of random physics facts, haha.

happy holidays, everyone :D