# Questions tagged [mass]

Questions regarding the property of astronomical objects that determines their inertial resistance and gravitational interaction with other bodies.

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### From an outsider's perspective, how can a black hole grow if nothing ever crosses the event horizon?

Due to time dilation, an outside observer never sees a falling object actually cross the event horizon. I'm not referring to the optical illusion of red-shifted light making objects appear to fade ...
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### Dark energy contributing to, or modifying, mass estimates?

I have found some papers (like this one: https://www.aanda.org/articles/aa/full_html/2009/45/aa12762-09/aa12762-09.html) which say that dark energy increases the potential energy in a system of a ...
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### If the universe is a closed spacetime structure, can we assign a center of mass to it?

If we envision the universe like a balloon but in 3D, is it possible, in general, to assign a of global center of mass?
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### How to calculate metallicity of a star that is made of iron of 20kg and Hydrogen 1000 kg?

I want to know how to calculate star metallicity using only masses of metal and hydrogen of the star. I am attaching my working so far. I am not sure how to exactly calculate the log10(Fe/H) based on ...
1 vote
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### Why do we estimate the Minimum mass when we are dealing with exoplanets?

While solving astronomy problems dealing with exoplanets, I always see that the question asks for minimum mass instead of the mass. Why is that so and why is the calculated mass minimum mass? example ...
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### Accurate formula for calculating the mass of an exoplanet using the transit method

A friend and I did some work on exoplanets with the help of a research institute (IEEC in Spain) for a major high school project. What we did was to "redetect" the exoplanet XO-6b through ...
1 vote
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### Approximately what fraction of the galaxy's stars are in the bulge? [closed]

In the text of the question it is said to consider density uniformly
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### Measuring the mass of the luminous matter in a galaxy

The mass of total matter in a galaxy can be measured using the rotation curve of the galaxy. However, how do people determine the mass of luminous matter in the galaxy, as a function of the distance ...
1 vote
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### Are there negative masses that attract each other but repel positive masses? [closed]

Is there law/rule in physics that precludes the existence of a negative mass, wherein similar negative masses attract but positive and negative masses repel? To keep this on-topic in Astronomy SE: Has ...
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### How is light unable to escape a black hole if photons are massless? [duplicate]

I understand light will follow the curved space that the BH is causing due to its mass. I also understand that mass attracts other mass but then photons are massless. So 0(photon) x m2 (the BH) is ...
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### When calculating the mass of stars, is it considered that additional mass could be added because of pair-production?

I would like to know that, since stars emit a lot of photons where some of them could be producing electrons-positrons pairs, if its mass affects the calculations, and if because of this is different ...
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### How much mass to make a shperical object?

I was googling around for info for D&D campaign I am going to run. I was wondering about the mass required for a object to pull itself into a shperical shape and it seems that the answer varies ...
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### What's the relationship between the mass of a star and the mass of its core?

What's the mathematical relationship between the mass of a star and the mass of its core? For simplicity's sake, I'm asking about the cores of main sequence stars at birth, and by "core" I ...
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### What actually is the mass? [closed]

Since high school, I've been told that the definition of mass is "quantity of matter" (which is absolutely wrong, I guess). If mass is actually a quantity of matter and it is a measure of ...
1 vote
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### is weight of two identical objects same when they have the same exact distance from earth's surface but one is on a mountain and the other on a plane? [closed]

Is the weight of two identical objects the same when they have the same exact distance from the earth's surface but one is on a mountain and the other on a plane? The distance between the plane and ... 616 views

### What is the (overall) half-mass radius of Milky Way

I am doing some simulation and I need the half-mass radius of Milky Way (total mass: including all objects, dark matter, nebula...), but I cannot find the value and I don't know how to calculate it. I ...
1 vote
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### Which KBOs would one have to merge in order to have more than half the Kuiper belt's mass?

I wonder how many and which Kuiper belt objects' masses would one have to merge so that the resulting mass is more than half the Kuiper belt's mass. The total mass of the Kuiper belt is reportedly ...
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### Is the sun's volume shrinking currently?

The Sun loses about 5.5 million tonnes of mass every second, does this mean Sun's volume is also going down? If so can we tell by how much every year? E: "by how much" I mean can we tell if ...
261 views

### If a black hole has the same mass as me, then why dont i suck everything at my center of mass?

So, a black hole is very dense that you can get really close to its center of mass that it has a strong pull, well, if i have the mass of a black hole that has a really small event horizon, why doesnt ...
1 vote
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### How likely are triple planet systems?

Is it likely to ever discover three planets of similar mass revolving around a common barycenter, or would such a system be too unstable? Such triple planet system would look like a triangle once in a ...
1 vote
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### If a black hole has a mass similar to a star, why does it have a different gravitational pull?

Say there is a black hole with 1 solar mass, having the sun's mass, it would have the same gravity as the sun, right? But it still has an event horizon, so why does it have such a strong gravitational ...
1 vote
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### Is there a formula to calculate any star mass from Luminosity, Radius, and/or Temperature (K)? [duplicate]

I know there is the Mass-Luminosity relationship, but I am wondering if there is a more accurate formula I can use based on the data points I have generated: Absolute Magnitude (based on class and ...
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### What is the density of the solar system per cubic light second outside the Jupiter ecliptic?

I have been unable to find any research on particle density over 1 cSecond above or below the ecliptic in regions with a gravitational field with an acceleration less than 1/1000 of meter per second ...
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### Is there a way to calculate the mass of of a stellar remnant given the initial mass of the star?

Assume there is a star in a completely empty region of space, away from any outside influence. Is there a way to calculate the mass of a resulting stellar remnant, a white dwarf, neutron star, or ...
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### Why don't we detect planets around OB stars and no terrestrial planets around A or early F stars?

Looking at an exoplanet database, I noticed that there are very few planets detected around main-sequence OBA stars, and most of them are gas giants/brown dwarfs. Why can't we detect low-mass planets ...
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### How do we estimate the dimensions and mass distribution of a galaxy's dark matter halo, beyond the effective limits of its visible matter?

Current research suggests that the Milky Way's dark matter halo may extend up to about 10 - 15 times the size of the visible galaxy, and is believed to be roughly spherically symmetrical. But I don't ...
1 vote
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### Is is possible for a main sequence star to have 0.77 solar masses yet only be 0.54 solar radii?

I know ordinarily a star's mass and radius tend to be proportional, so a 0.5 solar masses star tends to be about 0.5 solar radii and have a density of 4.82 g/cm³, 3.42 or about three and a half times ...
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### What increases or decreases the mass and density of a fixed radius star?

Assuming a relatively even proportion of mass and radius, a 0.25 solar masses and radii star would have a density of 22.5003 g/cm³, or about 16 times our Sun's density. Keeping the radius of 0.25 ...