As I understand it, both of these stars are covered with thick clouds of dust. One is in formation stage and other is in last stage of its life. How do astronomers differentiate which is which? My guess is they use spectroscopy and fond out what element is present on both of these systems to do it but I'd like to know more about it.

Usually calendars are zeroed by some arbitrary date, then count days since then. This requires continuous record keeping and the current date cannot be calculated otherwise. (For instance, the birth of Christ is now estimated to be in 4BC due to ancient errors in adding up the length of the reign of various kings, and in the summer since the Romans moved the date of Christmas.) A good epoch should

1. be a distinct, preferably instantaneous physical event,
2. the time since which should be precisely and scientifically calculable long into the future;
3. the precision of knowledge of that date shouldn’t degrade much with time,
4. precision of the date shouldn’t be possible to improve through more scientific observations,
5. it should be observed and well characterized by contemporaries.
6. it should not be owned by anyone, like a special 1kg mass in a bell jar.
7. ideally there should be multiple methods to compute its date
8. it should be considered acceptable

It should be ok to have the epoch some fixed offset from the physical event, such as shifting it to the GMT solar midnight of morning of—which then requires the time and longitude of the physical event to be known.

Some candidates for epochs: A) The date of the Crab Nebula supernovae SN 1054: Midnight GMT of July 4, 1054 A.D.. Advantages: it was observed by multiple contemporaries globally. It left a pulsar (the Crab pulsar PSR B0531+21), so there are two independent methods to calculate its age—through backtracking out flowing gas and from pulsar spin-down, where an initial spin rate can also represent age. Fits criteria 2, 3, 4, sort of 5, 6 (and how!), 7, 8. Disadvantages: The time of the initial event was not recorded by contemporaries, and even the date is subject to some debate (1) the physical event isn’t completely instantaneous. (5) Contemporary observations are dodgy ancient records. The Chinese astronomers who had the best records may have had a cloudy night on the first day, or otherwise not noticed it for a little while.

B) A solar transit of Venus (9 Dec. 1874, or 6 June 1781), particularly using the first or fourth contact time. Advantages: instantaneous event calculable long into the future, and well characterized at the time. There was even video of the former of the two dates. (The atmosphere of Venus isn’t much of a problem, and the black drop effect only interferes with 2nd and 4th contact). Seems to tick every criteria except maybe 7. Disadvantages: maybe only one way to calculate it.

C) The Trinity nuclear explosion (Midnight GMT of August 16, 1945), back calculated by radioactive decay rates. As the first fission product release, its date should be possible to calculate from diverse geological samples. It was abundantly characterized by contemporaries, and the exact second of the event is public knowledge. Advantages: ticks criteria 1 (and how!), 2, 4, 5, sort of 6, probably passes 7,

Disadvantages: partly fails 3 due to exponential radioactive decay. The US holds the site and will have the best data, so it partly fails 6, the nature of nuclear weapons may make it unacceptable, failing 8.

What other options can you think of for an epoch event that can be eternally observable start of a clock? Preferences?

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I don’t know a ton about astrophysics, so I might be missing something obvious.

Is it possible that the mass of a galaxy causes spacetime to curve into a bowl around it? If mass causes curvature, could lots of mass over a wide area cause a bowl?

When I imagine a bowl in spacetime, the edges have a pretty sheer curve, but it basically levels out at some point. My understanding is that dark matter seems to gather around the edges galaxies. I would think a more sheer curve in spacetime would have a similar effect.

Like I said, I don’t know much, so let me know if I’m way off base. It just makes so much sense to me.

I just saw today's Kurzgesagt video on Gravastars: https://youtu.be/BmUZ2wp1lM8

I have questions. Where is Dr. O'Dowd?

All of the questions aside as to if either and or both of black holes or gravastars exist, my brain immediately starts down the tangent of white holes. They should exist, but... is the interior of a gravastar just a white hole?

And if not, which is likely not, if gravastars do exist, which is a big if, what is the interior of a gravastar? If it really does contain a very large amount of energy, why wouldn't it do something? Why wouldn't there be a microcosm of activity?

I'm not an astrophysicist but I was asking if we make a bigger telescope does that mean we don't need to travel to 550 AU to use the Sun as a gravitational lens?

thanks

Hello experts - I love learning about astrophysics, and one of the things that blows my mind is the notion that Jupiter has a perhaps earth-sized core of liquid metal hydrogen whose rapid rotation and electric currents running within create the superpowerful magnetic field of the planet. My questions are: Does the magnetic field emerge from the surface of the liquid metal core; how does that field influence/control the environment at the boundary between the liquid core and the semi-gaseous atmosphere of Jupiter, and - while acknowledging that the luminance is likely zero or near zero, has anyone attempted to render or model what that might look like?

Many thanks in advance for any insights or pointers you might offer.

hey i have started reading astrophysics books and i could not find a clear explanation on what is pogson's equation is it stating that "the brightness of star 1 upon the brigtness of star 2 is equal to 2.5 into - magnitude of star 1 - magnitude of star 2

if i am wrong correct me

I would not say that I am a “huge” space/science skeptic, but something that I have an issue with that I imagine many other laymen do is that a lot of theories about the universe just simply don’t make sense from a common sense perspective. It seems to me that science often takes large leaps in unprovable or knowable ideas and those ideas end up being passed off as truth.

I will give an example of this that I would love an explanation for. So Earth is supposed to be spinning, while orbiting the sun, which is orbiting the milky way, all of which are supposed to be “ever expanding” into the universe. If that is true, then how have we been able to witness the same exact stars and constellations that were recorded thousands of years ago?

From a layman perspective, that just doesn’t make sense. If all of the above is true, and these distant stars that we see each night, which are not relative to Earths position, are also constantly in motion and expanding into the universe, then how is it that we can still see the exact same stars and constellations after all these years? I’ve posed this question to many friends and family. Some seem to understand my dilemma, others hit me with “well we are so far away it takes light a long time to travel”. Well that just doesn’t make any sense. I get that it takes light a long time to travel but shouldn’t that really only apply if the objects are stationary, or relatively stationary? When you have two bodies that are completely independent of each other moving and expanding in completely independent ways, how can it be explained that light could still reach us? Even more, in exactly the same places as it has for thousands of years?

If i need to try to word my question differently or better I will. I’m very curious and would love to hear some answers. Thank you

edit: thank you all for helping my monkey brain to have a better understanding. i will be looking into this more with the links and and terminology given to me but unfortunately am not smart enough to further participate in the conversation

If the Sun expanded at the speed of light (hypothetically speaking for the purpose of this debate) and stopped right next to Earth, would we see the expanded Sun immediately upon its arrival, or would it still take 8 minutes to observe the change due to the light traveling from its previous position?

If we still see it 8 minutes in the past, then how could we see it expanding at the speed of light even though the sun is now directly next to earth emitting light?

Obviously if the sun is expanding at the speed of light then the we wouldn’t see any light emitting as it would travel at the same speed, so could it just be we see 8 minutes of darkness then suddenly a massive sun in the sky?

What are your thoughts, my fellow genius people.

Hello all:

I'm actually an astrophysics undergrad (subsequently went off into engineering) so I have a pretty solid understanding of a star's journey through the HR diagram. However, I've been reading some books on stellar evolution lately and been realizing that, while it is well understood WHAT happens from a mathematical and computational perspective- i.e. the star grows in luminosity and radius and cools considerably - there does not seem to be a consensus on a straightforward qualitative explanation of exactly why this happens.

For example, from Ryan and Norton's book Stellar Evolution and Nucleosynthesis:

"Numerical evolutionary models that incorporate all of the known contributing physics reproduce the observations very well, so astronomers have confirmed that they understand the process sufficiently well to be able to reproduce it on computers. However, despite this triumph, one regrettable problem persists: it has not yet proven possible to reduce those processes to just a few simple statements that encapsulate the major physics driving this phase of evolution. It is possible to point out parts of the contributing physics,but these always fail to provide a robust explanation of what takes place."

I have found this quite surprising and something that I think most books and lecturers gloss over. Has anyone come across a robust qualitative explanation of the steps driving red giants to expand (i.e. a why as opposed to a what)? I've seen description of the "mirror principle" and an appeal to the virial principle, but these also are really descriptions of "what happens" rather than "why it happens".

Like dark matter requires, these virtual particles can only be detected by the distortion of space time they create a distortion which continues to propagate after the pair's destruction. Thanks

I have two questions: (1) when people talk about the radius of a neutron star, how do you know if they are referring to the surface radius or the emission/radiation-region radius?  (2) Can the radius shrink if the neutron star is accreting mass and perhaps transitioning to more of a quark-gluon soup in the core?

Here is some context on the radii of neutron stars and different ways to estimate that important figure.  As with my previous post on neutron stars and their mass, I welcome and seek corrections and better explanations.

Relative to their enormous mass -- as much as one to two Suns -- neutron stars are pinpoints in space.  The radius of one of those hyper-squashed stars cannot exceed more than about 12 km (7.4 miles). If their girth were larger, their gravitational force would collapse them to a black hole. The likely radius ranges somewhere between 10.4 and 11.9 kilometers. Stated in Earth terms, the sphere of a modest neutron star couldn't nestle in the Santorini, Greece caldera, which has a radius of 5.5 km north-south, but might squeeze into the Crater Lake caldera, in Oregon, which is approximately 8 kilometers (5 miles) north to south and 10 kilometers east to west.

Paradoxically, more massive neutron stars may have smaller radii. It depends on the uncertain relationship between pressure and density. The measured mass range for neutron stars is 1.17-2.1 solar masses, so given what is known about mass-radius relationships, you could estimate the smallest possible radius from a model curve. For the "softest" equations of state, where quark matter develops at the core, the smallest radius for a 1.17 solar mass neutron star is about 8.5 km. 

Because of their diminutive stellar size (and low luminosity), neutron stars are almost impossible to spot other than with specialized instruments, which presents challenges to measuring their radii. Directly measuring the radii of neutron stars is incredibly difficult. The "measurements" that exist are indirect inferences and have large uncertainties. Here are some of the methods for estimating the radii of neutron stars.

* X-ray emission: Astrophysicists can collect X-ray emissions from the surface of accreting neutron stars in binary systems and associated burst phenomena, involving explosions of accumulated material. Although complex characteristics need to be understood (including the composition of the neutron star atmosphere), these mass-radius results are beginning to constrain the theory.  The radius measurements have largely resulted from X-ray observations of NSs in low-mass X-ray binaries from telescopes like NICER and XMM-Newton. 

* Thermal emission: Heat radiation from the surface of the star allows us either (1) to measure its apparent angular size or (2) to detect the effects of the NS spacetime on this emission -- and thereby extract the radius information. The approaches can broadly be divided into spectroscopic and timing measurements. They are generally based on the assumption of blackbody radiation. [Bandyopadhyay, D. and Kar, K. *Supernovae, Neutron Star Physics and Nucleosynthesis*, Springer 2022 at pg. 52]

* Scintillation: Analyzing the periodic brightness oscillations originating from temperature irregularities (anisotropies) on the surface of a neutron star can enable calculations of its radius. The amplitudes and the spectra of the oscillation waveforms depend on the NS spacetime, which determines the strength of the gravitational light bending the photons’ experience as they propagate to us, as well as on the temperature profile on the stellar surface and on the beaming of the emerging radiation. Using theoretical models, the properties of the brightness oscillation can, therefore, be used to probe a star’s radius. 

* Gravitational waves:  There are also significant prospects for radius measurements from Advanced LIGO observations of coalescing NS binaries. The characteristic frequencies of these waveforms can be used to obtain information on the NS radius.

 * Hot spots:  A recent method to derive mass and radius is to observe the emission of hot spots on rotation powered millisecond x-ray pulsars. This is done by the NASA instrument NICER, positioned on the ISS. The output of NICER is a pulse profile sample of phase vs energy. This is combined with a light curve model of emission and relativistic ray-tracing to arrive at a radius figure.

* Gravitational redshifts: Instruments can observe absorbed lines in gamma-ray bursts from the surface of the star. This is also applicable for x-ray bursts from binary neutron star systems. This method has not been very useful, however, and has only produced one neutron star GS 1826-24 with the vague result of a radius less than 6.8 − 11.3 for a solar mass of < 1.2 − 1.7.  

* Moment of inertia.  If scientists can calculate the moment of inertia of a binary neutron star, which is a measure of how resistant the star is to changes in its rotational motion, further calculations can estimate the radius of that star. [Bandyopadhyay, D. and Kar, K. *Supernovae, Neutron Star Physics and Nucleosynthesis*, Springer 2022 at pgs. 54-55]

Hey!

I really hope that this post doesn't violate any rules of this subreddit.
Well, I saw that one of my favourite popular-science authors just released some signed copies of his books for the standard price. I would love to buy one or two, but the shipping fees to my location (Germany) are astronomical (109$ for a 18$ book). Is there any friendly US-American out there willing to help me? In this case I could send the book(s) to your address or a postbox and send you the money for the shipping to Germany plus a bit of extra for your efforts!

I know this can be a bit risky, because worst case I will be scammed out of my money, but it might be worth this risk.

Thanks!

Could it be that so called visible universe is something like a specific wave lengh of matter that we can observe, and if we could somehow tune in on to different wave lengh, we would see that the Big bang wasnt actually the beginning of the universe, and that it have a bigger size? By wave lengh i mean something like a different dimension, something in the category of scale rather then the light. Could a dark matter or dark energy be such thing?

saw a video of a guy talking about the speed of light. he said it would take around a minute to go to insert name here galaxy if we travelled at the speed of light. so thats 180,000 km away.

he said if you come back to the earth (i assume another minute travelling on the speed of light) 4 million years would have passed on earth.

i cant wrap my head around that idea. my head keeps telling me only 2 mins plus some time spent in point B has elapsed. how would 4 million years pass when you only travelled 2 mins?

would that mean that if a photon from 3,000km reaches the earth from the source in 1 second but from the start of its journey till it hits the earth more than 1 second passed?

If you were shrunk down to a size that is smaller than an oxygen molecule how would you breathe? If it was possible to be shrunk to that size.

I was reading a research paper and came across this:

“The sedimentation of neutron-rich material in turn leads to a ≃8% increase in central mass density and thus a concomitant release of gravitational energy. The global stellar structure is also affected: the radius of the star decreases by ≃1%, which represents a sizable fraction of the residual cooling-induced contraction of high-mass white dwarfs.”

Why is that? Is it because electron degeneracy pressure?

Hello, I have a Statistics class and we have a project where we run a linear regression model on some data set, and I was thinking of doing something interesting like Globular clusters, but I wanted to see if you guys could let me know if you see anything of value in this idea or if there's a problem. So I found a data set that has all the globular clusters in the Milky Way with various stats about them like diameter, radial velocity of the cluster, distance from center of Milky Way, distance from sun, brightness, and absolute magnitude. I was wondering if you think it would be interesting to use linear diameter as the dependent variable and then try these as predictor variables? So the project will basically be seeing if intrinsic aspects of the cluster like brightness will have a stronger association with linear diameter than something extrinsic like radial velocity and distance from the center of galaxy. Again, I don't know anything about astrophysics so please tell me if this is stupid.

Can anyone fact check this? If this is accurate, I have some follow-up questions:

“Yes, there are times when the Moon passes through the constellation of Hercules, although it is relatively infrequent. The Moon’s apparent path across the sky, called the ecliptic, is inclined about 5 degrees to Earth’s orbital plane. This means the Moon can wander up to about 5 degrees north or south of the ecliptic.

Hercules is not one of the traditional zodiac constellations through which the ecliptic passes, but it is located near the northernmost point of the Moon’s path. Specifically, Hercules spans a declination range from about +12 degrees to +51 degrees. During periods called major lunar standstills—which occur roughly every 18.6 years—the Moon reaches its maximum northern and southern declinations, up to about +28.5 degrees and -28.5 degrees, respectively.

When the Moon is at its maximum northern declination, it can pass through the southern parts of Hercules. Therefore, although it’s not common, the Moon can indeed be observed within the boundaries of the constellation Hercules at certain times.

The last major lunar standstill was 2006, so 2025 should be the next opportunity! You will be able to see the moon cross Hercules once a month!”

Thank you :)

Subject experts in SPH, what kind of astrophysical fixed body systems I can use to test the Preservation of angular momentum in SPH and it should be not computationally heavy. Give me some ideas.

friends,

long story short, i enjoy programming and ended up making a message board a-la hacker news. it is themed around space sciences and astrophysics. it was fun and i think it turned out pretty decent.

i'm wondering now if i should go through the hassle of putting it out there and promoting it, or just let it go. it would be a place to post and discuss research papers, code, blog posts, and job positions. i'm torn D: on one hand, i've often found myself with a new paper or codebase, wanting to share but not really knowing where to put it. i feel like having a dedicated place for this would be cool. on the other hand, we already have several options. off the top of my head i can think of linkedin, hacker news and reddit. all of them feel off for some reason though - i despise the "culture" and mindset of linkedin; i like hacker news but it has a completely different focus on tech; and reddit just doesn't feel right for this.

so i wanted to hear from other research people. what do you think? would an independent message board benefit our community?

Please, dont respond with slang or any other high-level words in English, as English isnt my home language. Thx

I found an unusual correlation and wanted to get some feedback or insights. Here’s a summary of what I’ve done so far:

I divided the Ocean Niño Index (ONI) dataset (1950–2024) into periods when Mars was "in range" (Mars-Earth distance less than both Mars-Sun and Mars-Venus distances) and periods when it was not. The mean Niño Index is consistently lower when Mars is in range.

To ensure this isn’t simply due to seasonal variations, I compared the Niño Index separately for each month over the dataset’s entire timeline. The difference persists even after accounting for seasonal effects.

Could this correlation have a natural explanation? For example, could subtle gravitational or tidal effects from Mars affect ocean or atmospheric dynamics, or might this align with some other known climatic driver?

I’d appreciate any ideas or feedback.

I'm curious about how angular momentum is distributed in the universe.

Is the axis of rotation of different galaxies totally random?

Do solar systems rotate the same way as their galaxies?

Do galaxies rotate around each other?

thanks

I’m working on a science fiction story set on earth in a fictional time of increased solar weather. I'm trying to figure out what this would look like and what consistent luminous structures might be present in the sky so I can know where the science ends and the fiction will begin. My wheelhouse is molecular biology, so I know my way around a terrestrial ion but I get a little lost when the ions become plasma in the vacuum of space moving across vast distances.

What would it look like and how plausible would a continuous coronal mass ejection be, such that the geomagnetic field would constantly be disturbed by 1-2uT, like a permanent Carrington Event? Assuming there were no satellites in orbit or conductive wires on the planet, how would that affect life on earth? Is it plausible that the sun could ever eject such a significant amount of coronal mass that it could overcome the geomagnetic field in a dangerous way to terrestrial life?

From what I've read so far it seems to me that the most obvious impact, and perhaps the only impact, would be aurorae. But as I read up on aurorae it's not clear to me if they’re primarily powered by ions that come through the bow shock down the magnetospheric cusps (and why such aurorae tend to occur more often in the north) or from ions flowing back in the tail’s plasma after magnetic reconnection, and how or if that changes when CME is a significant weather factor compared to the usual solar wind. Along the same lines (pun not intended) would the magnetic reconnection in the tail ever be luminous and visible from the night side of the planet? Magnetic reconnection is commonly illustrated as an explosion of light in both the earth's magnetotail and the sun's photosphere but I can't tell how much artistic license is involved.