I'm writing a paper and mentioned in the introduction that dwarf galaxies in denser environments are more likely to be quiescent. This is a fact that's been well-established for some time, and there are tons of papers going back decades backing this up. New papers pop up every few months that reassert this. I want to cite appropriately, but I'm not sure how far back I should go! Should I:

1. Try to find the original paper that first makes this claim and cite it?
2. Find the last ~5 papers that corroborate this finding to ensure my citations are recent?
3. A secret third thing?

I ask in this thread because I know the conventions for what is considered a recent citation and what is not depends on the field, and want to know the convention is for astrophysics (specifically galaxy evolution). Thank you in advance :)

I’ve always been really curious about the universe. Like how any of this even exists in the first place and what we actually are in the middle of it.

I’m especially curious if people who study this from a scientific side, like astrophysics or neuroscience, ever find themselves drifting into more philosophical territory with it. At some point, does it stop being just facts and start raising bigger questions for you?

I started a small discussion group last year because I wanted a space to have these kinds of conversations that don’t really come up in day to day life. It’s been going really well, but most of us come at things from a more introspective or spiritual angle. I want to hear from people who think about it differently.

Just to give an idea of what we talk about:

•consciousness and whether it’s just the brain or something more

•what reality actually is vs how we experience it

•time, space, and how any of this even works

•whether things are random or if there’s some kind of pattern

•intuition, gut feelings, and those weirdly accurate moments

•dreams and altered states and what might be going on there

•human behavior and how we make sense of things

•manifestation and where the line is between
mindset and something more

•moments that feel unexplainable or bigger than us

•how much of our experience is shaped by the brain

•the gap between what we know and what we feel

It started local to the DC area but is now mostly virtual. Anyone can join (we currently have members from other countries and I’m committed to making it work)

So if you think about this kind of stuff or have your own perspective, I would really like to hear it!

If humans made a wormhole, would it be affected by velocity and gravity or be locked into one point in space?

And if we did go through a wormhole and the other end was in another galaxy moving at a very different speed wouldn't that be like jumping from one moving train onto another moving train but in the opposite direction and multiplied by possibly millions?

Hi r/astrophysics,

I have little no knowledge about Mar's interactions with h2o, but thought I'd make a guess now that I'm learning about planetary formation. Any insight or critique is very appreciated!

I'm guessing that there are two possible phases during which Mars might have sustained liquid water: It’s planetismal stage, during which it might have been far enough past the frost line before being sling shotted closer to the sun, OR during it’s primary atmosphere, when the atmosphere was dense/complex enough to compress/heat the h2o. 

Again, any critique and insight is appreciated.

I was thinking about the infinite universe. Assuming we can figure out when the Big Bang occurred and we know the expansion rate of the universe, wouldn’t we be able to extrapolate, with pretty good accuracy, the size of the universe? is this where we get the idea that the universe is 93 billion light years across? Wouldn’t this give us an idea as to the boundary of the universe?
Pardon me if this is a stupid question. I am definitely not a physicist, but I do admire their work.

Been reading through some papers on dark energy models and keep running into the emphasis on pinning down w with more precision - specifically whether it's exactly -1 (cosmological constant) or drifting slightly above/below that

I understand qualitatively that w < -1 implies a "Big Rip" scenario and w > -1 implies something closer to gradual deceleration of expansion, but I'm struggling to grasp why such a small deviation from -1 (like the DESI results suggesting w might be evolving) has such dramatically different long-term implications

Is the sensitivity here more about how w compounds over cosmological timescales, or is there something about the underlying physics (quintessence vs. cosmological constant) that makes even small deviations qualitatively different rather than just quantitatively different?

See also: The publication in the Astrophysical Journal Letters

Hello!! Not experienced in this at all, so forgive me if I get things wrong, that's actually why I'm here!!!

Edit: GO CHECK THE OTHER EDIT!!! THE STUFF BELOW THIS BEFORE THE EDIT ISNT REALLY IMPORTANT ANYMORE, READ IF YOU WANT THOUGH!!!

So I'm writing a book that takes place on a different planet (technically all 'aliens' no human appearance) and I have a few things set in stone. The main planet, zophlyn is green 💚, and it's brother planet adrith is the bigger grey 🩶 one. Zophlyns orbit is crazy slow (like over hundreds of thousands of years for a full rotation, I'm taking some creative liberty on this part)

Main point is zophlyn is in the shadow of it's brother planet, I did this bc I wanted a mostly dark atmosphere without taking away the stars. The thing that I'm having trouble with is one of zophlyns moons, the blue💙 orb (no official name so I'll just go with blue)

Part of the problem in my book is that zophlyn does not rotate and it's back is getting slowly torn up by adriths gravity. I want zophlyn to have moons, especially one that reflects the sun onto one part of the planet to make sort of a setting sun vibe. I have an arrow of that moon (blues) rotation, would the gravity interfere greatly with it? Spacing isn't really my concern, I know I didn't go very accurate, I just want to know if what I'm wanting is possible!!

Edit: OH MY GOD I JUST HAD AN IDEA!!! so I'm being told that zophlyn orbiting adrith won't work, would it be possible for me to have zophlin orbiting the main star, but the same speed so it's just stuck in adriths shadow? I'm cutting out the part where it gets pulled apart by the gravity, I'm changing that bit, but now my only question is is it possible to keep zophlin the same speed as adrith?

Hello there, Iam Bavotreq/Flutterzance/Durna

I did my first animated video on space, it's about Venus. I hope it's professionnal, I am trying to improve my content despite multiple mistakes and inaccuraties :

https://www.youtube.com/watch?v=12n3TpF3R7A

Thanks in advance. I admire all of you for knowing this stuff and for being able and willing to explain it. :-)

I’m a high junior trying to get research opportunities or really anything for astrophysics. I have previous knowledge through programs and a planning to take the ap exams for physics 1 and 2, i’m also gonna take physics this year. What are some ways to get opportunities?

How big/strong does one must be so be able to push outwards from the Sun's core to make it explode?

Ignore biology and stuff like heating or being crushed by the pressure

I hope this is the correct place 😬

For those who have applied to a Roses proposal call, what is the timeline for hearing about acceptance or rejection? I submitted something to HTIDeS this spring and I'm curious about the timing. Its up in the air how long I'll be at my current institution, so I was just curious

Hey all,

I recently graduated from Aerospace Engineering and I’ve been teaching myself computational physics on the side (built a 2D incompressible Navier-Stokes solver from scratch — projection method, particle tracking, the works) and I’ve caught the orbital mechanics/astrophysics bug hard. I want to pivot my self-study and eventually my career in that direction, but I’m coming at this from outside the traditional pipeline, so I’m looking for advice.

Projects I’ve got planned so far:

1. N-body simulator (leapfrog/Verlet integration, want to do it properly — symplectic, energy-conserving)
2. Orbital mechanics toolbox (two-body, maybe perturbations, Lambert solvers eventually)
3. Telescope image processing pipeline (calibration frames, stacking, etc.)
4. Astrometry — measuring position shifts of stars across telescope images (proper motion / parallax type stuff)

What I’m stuck on:

1. What other projects would actually make me look competitive for astro-adjacent roles or research assistant type positions? I have a strong numerical/scientific computing background (PDE solvers, CFD) but zero formal astro coursework. Is that a plus (rare + useful skillset) or does it not matter without the domain background?
2. The internship problem — most of what I’m finding is aimed at current students. I’ve already graduated, so I’m not sure what the equivalent is for someone in my position. Are there postgrad/early-career programs, or is that door mostly closed until I’m enrolled in something again (e.g. a master’s)?
3. Would cold-emailing labs to volunteer actually work? I keep seeing this suggested but I don’t know if it’s realistic or if researchers actually take unsolicited volunteers seriously, especially from someone without an astro degree. If it does work, what makes an email like that worth replying to versus getting ignored?

Any input from people who’ve made a similar switch (especially into computational/simulation-heavy subfields like orbital dynamics, N-body, or astrometry) would be hugely appreciated. Trying to figure out if I should be building a portfolio, applying for a master’s, or both in parallel.

Thanks in advance.

Hi everyone, I'd love to start getting into astrophysics and Astronomical Instrumentation.

I don't have a background in physics (but I do have the calculus thankfully) and I am planning to learn it myself. Does anyone have any recommendations for reading, YouTube videos or anything else I can use to learn?

Thank you in advance for the help :)

Hello can someone provide me with a study regarding existence of matter before the big bang theory? I am not familiar with astrophysics at all, just came from an online debate. According to cosmic history by NASA matter was created after cosmic inflation, however i struggle to find any scientific papers regarding it. Thanks a lot!

Here is the story so far as I understand it:

A cloud made largely of hydrogen and helium goes boom in space, causing a huge supernova. Heavy metals are made as atoms torn asunder, and matter gets ejected into the universe, creating gravitational waves and just about every known form of radiation. A beautiful thing, rare to behold.

But then something happens that I currently don't understand.

Matter decelerates. From what resistance, I still don't know because it's in a vacuum and I don't yet understand what's stopping it, but as this occurs, a gravitational core forms and that decelerated matter becomes fuel for the star.

As a reasonable man with a slightly better than average interest in real science, I currently understand that an object moving in a vacuum should have no resistance and should continue moving along it's trajectory until acted upon by another force (one of Newton's laws if I remember correctly). So if the boom is symmetrical, say for modeling purposes, the only thing that should stop it or slow it down is whatever it collides with, right?

So, 1. where does the resistance come from?

And then, 2: how does an explosion, which I understand to be an outward, exo thermal force that wants to throw everything away at the speed of instant, create a gravitational pull?

That is all at this time. Thank you in advance.

I know M⊙ means solar mass (x * the mass of our sun) but what does that M with a little star mean?

Paper: Morpho-kinematic of galaxies at cosmic noon

Something's been bugging me. We say dark matter + dark energy make up ~95% of the universe's energy budget, and ordinary matter is just a "5% rounding error." But that framing implicitly treats "the universe" as if it's mostly stuff, when really we're describing two completely different categories of unknown that happen to get lumped into one percentage.

Dark matter behaves like actual matter-it clumps, it has gravitational effects consistent with a particle or particle-like field, it plays nice with structure formation. Dark energy is essentially "whatever is making expansion accelerate," and we don't even know if it's a substance, a property of spacetime, or a sign that GR itself breaks down at cosmological scales.

Lumping them together as "the dark 95%" makes it sound like we're 95% ignorant about one mystery, when it might be more honest to say we have two separate, unrelated mysteries-one that's "matter-shaped" and one that might not be a thing at all in the way dark matter is.

Does anyone else think this framing in pop-sci (and even some papers) oversimplifies to the point of actually confusing the public about what's genuinely unknown vs. what's just unseen?

Title

So basically, this is an alien that has a very wide variety of temperatures and habitats across it because of its staggering size compared to earth. There’s also large caverns inside it that can make an almost hollow earth sort of aspect to it so not only do things live on the Earth, they also live inside of it. Here’s a list of everything you need to really know about it and also explain to me.

- the planet is about x4 the visual size of earth but the mass is only x2

- i’m not sure what kind of solar system that would need to be in to do the wide variety of temperatures so if someone could figure that out, I would appreciate it.

- the planet is dominated by mostly reptiles, some crustaceans, fish, and mysterious forms of avian/marine mammals, with minimal to no basic land mammals. This is to hopefully prevent the evolution of a high intelligence species that would make a replacement for humans.

- the hollow Earth bit is done with large open caves that tunnel into each other around most of the planet. Not like many other hollow earth concepts where giant layer of dirt floats over the core planet or is supported by outrageously small pillars.

Holographic Universe Theory, Simulation Theory, Multiverse, Quantum Immortality and so many others.

I feel like the information about them are scattered here and there. I'm listening to the Star Talk Podcast, have read a few books in the past, watch videos, or get some random google recommendations. Through one of them I learned about a theory that our universe could actually be inside a black hole.

But is there something like an encyclopedia for things like that? Surely there are several theories I don't know about.

And also: Where do you guys get your information beside reddit to stay up to date for the latest revelations?