Astronomy and Cosmology

Can Sirius go supernova after thousands of years and what would happen? I'm very curious to figure it out. I read Calvin Belk thought on it and he says that What do you think of it?

Mars gravity is 3.721 m/s2, which is about 2.65 less than Earth's gravity How could Mars low gravity problem be solved?

What is dark matter and what we know about it?

Happy New Year to all. It's December in London and Orion would look lovely if I had a clear sky once in a while. Why though on a printed sky balloon that I have, is Orion below the Horizon and not above? I know I'm missing something, please help. Best Confused amateur night time sky watcher

This thought experiment attempts to show how cosmological redshift is NOT a Doppler effect. Let's imagine that the universe expansion, for some dynamic reasons such as strange behavior of dark energy etc., is highly non-uniform, i.e. it stops and goes. Just for the purposes of this thought experiment. At the time when the universe is not expanding, some far away galaxy emits light. While the light is in transit, the universe expands for some time and then stops again. At the time we observe the light, the universe is not expanding. The source and the receiver do not move relative to each other at the time of emission nor at the time of reception. Thus, there is …

Just a little observation that we, humans, are not "infinitesimally" small on the universe scale, as often presented. We are rather above the midsize. First, I take Plank length as a natural unit for size. Second, I make comparisons on a logarithmic scale, because this is the scale that makes sense: 1 mm to 1 m is the same as 1 m to 1 km. In these units and on this scale, we are of 35 orders of magnitude in size, while the observable universe is of 62. This makes our size M+.

Hi everyone! sending this from my home country of up north Quebec. i wanted to ask this community about the job market. im starting my Astrophysics degree at the UdeM, i have still 2 years before my Masters. what are jobs in the field like? what is placement % ? what am i to expect in the comming years? i might ask more questions in the comments down below. I know that in canada and by extention Quebec, has a lot of Observatories and good labs. I would love to work in some observatory, but i imagine its really hard to land a position? I would also love to work in a plasma lab, as I feel that region of Physics has the most future as for work. …

Imagine a box with internal walls covered with mirrors. A light /photon bounces inside the box from mirror to mirror. The box is placed far away from gravitating bodies, somewhere in the homogenous and isotropic universe. As the universe expands, will the light inside the box redshift? (My answer, No.)

The idea is rather old: we put a bunch of Al foil 10 microns thick and reflect the solar flux over the daytime part of the planet. What sea level area will be shaded by 1 km2 of such foil at an altitude of 1000 km? Does it make sense to raise such an umbrella on the Geostationary orbit?

Why is it often said that "time itself started with the Big Bang"? If you take the scale factor in the Friedmann–Lemaître–Robertson–Walker metric to zero, then the spatial component goes to zero, but not the temporal one. In other words, space contracts, but nothing happens to time. Or, in the words of A. Zee, "In our current description, space is created at the Big Bang, but not time." (Zee, A. Einstein Gravity in a Nutshell: p. 787). So, any idea from where the notion of beginning of time in BB comes from?

While Elon is on its way to use CO2 to produce rocket fuel, I've got another question. Is it actually possible to reduce plastic waste into rocket fuel?

Recently I started a topic here in the attempt to explain the galactic redshift without the notion of 'space expansion', which was immediately moved to Speculation by a moderator and closed on the basis that I could not explain the MECHANISM which makes light to loose energy over vast distances, and therefore my whole theory (which is actually based on Fritz Zwicky's tired light) was unsupported and not worthy of consideration because of this. Actually I tried to explain it by saying that the mechanism is Dark Something, a mysterious phenomenon which science has not yet discovered, as I understand from Mainstream Science this a very good and entirely plausible explan…

In physics, acceleration is the rate of change of the velocity of an object with mass with respect to time. In physical reality, since F=ma, only objects with mass can accelerate, and objects without mass can't, because there is no mass to accelerate. In cosmology, however, SPACE ITSELF has ACCELERATION (attributed to the expansion rate of space itself). If space is not an actual object with mass (but a mere geometrical concept, which expands for no explainable reason), then WHAT exactly in this 'expanding space' is accelerated, and by what ? Let me guess, it's dark, it's mysterious, and it's everywhere in space. And it's having a really bad day at physics…

The title of this thread is the title of chapter 6-3 in the Richard Feynman's book, Six Not-So-Easy Pieces (1963). (This post is related to the discussion in one other recent thread, but not to its OP.) Here is the quote (pp.125-126):

https://www.nasa.gov/feature/the-universe-s-first-type-of-molecule-is-found-at-last The first type of molecule that ever formed in the universe has been detected in space for the first time, after decades of searching. Scientists discovered its signature in our own galaxy using the world’s largest airborne observatory, NASA’s Stratospheric Observatory for Infrared Astronomy, or SOFIA, as the aircraft flew high above the Earth’s surface and pointed its sensitive instruments out into the cosmos. When the universe was still very young, only a few kinds of atoms existed. Scientists believe that around 100,000 years after the big bang, helium and hydrogen combined to…

Since I understand that there is a very high standard on this forum which requires a mechanism for every theory, and not just an ideea, then I think you too are required to respect your own standards and give a mechanism for the theories that you support. So what is the mechanism that you propose for the Big-Bang ?

ISS astronauts recorded a video to wish a Happy New Year https://tass.com/science/1383067 Happy New Year! Wish you good luck and persistence during next year!

DM is as yet an unknown form of matter that is needed to explain anomalous rotational curves of galaxies, as well as structual galactic formation in general. Without it, means that our whole picture and theories about gravity is wrong. That is viewed as unlikely as it works so well in all other aspects...hence the unknown missing non baryonic mass hypothesis. In actual fact the name DM is more an expression of cosmological ignorance then anything else, much as the old ancient cartographers often marked unknown regions of the world at that time, as "terra incognita" The best observational evidence we have for non baryonic DM, is the bullet cluster anomaly. …

The observable universe is said to be about 96 Billion light years in diameter! But after the Big Bang when space was created it might have expanded into Infinity? Space itself without mass or energy is not limited to the speed of light c! So what stopped it expanding into Infinite size? Of course size is not really the correct term but you get my drift?

Have been watching the BBC'S Universe( ) One of the 5 parts is about BHs. Apparently they may radiate away to nothing(?) and what "next" is unknown. But I wonder about what might go on at the centre. Might "centre" not be a meaningful concept? Anyway, the force of gravity at the centre of the Earth (if it was a complete homogeneous sphere would be zero ,wouldn't it? Why does that not apply to a BH?

Is it possible that in a certain region of the galaxy there was a series of supernovas of massive stars, creating a second generation of massive stars that also went supernova after only hundreds of millions of years. And this process continued more times than our solar system did. Is it possible that matter that is heavier than uranium could have been created? If there existed elements, in other solar systems, heavier than uranium, could we detect it?

I realize that the space is a vaccum but the laws of physics still are there with gravitational waves so in theory for every action there is an opposite reaction so that means that all planets will shift won't they?

It is? I thought it was basically a big science fiction subject. I have heard the importance of a magnetic field to keep an atmosphere, but then I think of Venus which has an absurdly dense atmosphere and almost no magnetic field. So how important can it be. If this last part is considered a hijack please disregard, that was not my intention.

Would it make sense that if a second or third gravity well were to affect the planets in our Solar System, the orbital planes would be oriented toward them? For example, they might align with the center of the galaxy, but if a new gravity well came closer it might affect Pluto earlier than the others? (or to a greater degree to begin with.) Smaller objects like comets might even be affected to a greater degree to begin with. However, how long they have been in the solar system would be a factor of their plane too.

https://www.youtube.com/watch?v=899Wypv4rd0 There are very many planets that are capable of creating life forms but far fewer that have stable enough conditions to create sophisticated life forms. Is it possible that the life forms and civilization we have presently on this Earth could be the only such example anywhere in the observable universe? If that was to become apparent ,what lessons/revelations** could we draw from such an understanding?(would it be a deeper conclusion than from that there were other civilizations/cultural edifices elsewhere in the observable universe?) **not in any religious sense