# Tag Info

Accepted

### Are new stars less pure as generations go by?

The chemical enrichment of the Universe over time is indeed a thing. The plot below (source) shows observational measurements of the cosmic density of ionised Carbon in the Universe against redshift (...
• 3,070
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### If two white dwarfs collided, would they become a star?

The answer to your question is both yes and no, depending on the circumstances. Two white dwarfs colliding would likely yield a Type Ia supernova, assuming the combined mass exceeded the ...
• 33.7k
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### How can many stars be formed from the remains of one supernova?

Stars don't "come from" a supernova. Stars come from the interstellar gas in the galaxy, particularly where it is more concentrated into nebulae. This gas is mostly hydrogen and helium, but ...
• 87.6k

### Could stars form outside of galaxies?

Yes, stars can form outside galaxies if the conditions are right. An impressive example is D100, a galaxy that is moving through a cluster so fast that the ram pressure from the ambient gas forces ...
• 10.2k
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### How did the lighter elements end up in the center of the solar system? Solar System Formation

The solar system contains very little of elements heavier than Helium - less than 2% by mass. This is reflected in the chemical abundances measured in the photosphere of the Sun. i.e. The Sun does ...
• 114k

### How can many stars be formed from the remains of one supernova?

The mean mass of a star in a typical star forming region is about 0.3 solar masses and contains about 1% by mass of elements heavier than helium A typical core-collapse supernova progenitor might have ...
• 114k

### Does the Sun rotate?

Although its too late to reply to this interesting question but trying to add few more points. Yes the sun rotates. Now the question arises as to how we can check that? We can observe this by ...
• 281
Accepted

### Which came first: Galaxies <=> Stars <=> Planets?

The structure we see in the Universe has formed from the gravitational collapse of the matter that was once an almost smooth density field of gas ("baryons") and dark matter$^1$. The word &...
• 31.9k

### Why can't 'dead' galaxies start forming stars again if they merge with another, 'active' galaxy?

It is not true that "dead", or quenched galaxies cannot start forming stars again. It is called rejuvenation and is observed occasionally (e.g. Chauke et al. 2019), although not commonly (...
• 31.9k
Accepted

### Why does a hot cloud need more mass to collapse?

It's more do do with having a higher pressure gradient than a higher pressure, though for a cloud of a set size, the two are equivalent. For a cloud to be in equilibrium requires  \frac{dP}{dr} = - ...
• 114k

### How are binary star systems created?

There are two main theories for the formation of binary stars - one accepted, and one mainly deprecated. The fission hypothesis. The fission hypothesis states that the binary system forms after the ...
• 33.7k
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### Which stars did the Sun form with?

Most stars form in clusters, so it is very likely that the Sun was part of a star cluster when it formed. But in On the Dynamics of Open Clusters, the relaxation time of a cluster is calculated to ...
• 3,311

### Could stars form outside of galaxies?

It's quite possible for stars to form outside of galaxies, typically in environments where large amounts of gas have been stripped from a galaxy. This usually involves either a tidal interaction with ...
• 33.7k

### Are there heavenly bodies between galaxies?

The Big-Bang was not an explosion in empty space. Inter-galactic space is not empty, there is an inter-galactic medium, gas clouds and material ejected from galaxies, including stars and possibly ...
• 3,236
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### Why do stars rotate slower than they're expected to?

There are two phases to this problem. In order to accrete into stars, a huge amount of angular momentum must be lost to allow so much mass to gather into a small volume. A second problem is how stars ...
• 114k

### How many generations of stars can be formed in the Stelliferous Era?

One can make a theoretical upper bound by considering the most short-lived star possible $\tau_{short}$, and a large supply of initial hydrogen $M_H$. Then one could calculate the fraction hydrogen ...
• 10.2k
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### What is meant by "Radial Direction" of a galaxy?

'Radial direction' typically means from the center, moving outwards. Typically, these kinds of studies will break a galaxy up into several annuli, or rings, and examine the star formation activity ...
• 196

### Could the earth become a star if more mass was added?

Regarding the title: Yes. Does this mean that the star started off as a planet? Yes, a star could technically start out as a planet, if it accreted enough mass. However, this is extremely unlikely,...
• 7,682
Accepted

### What is the origin of the dust near the sun?

There are two primary dust populations near 1 AU, interplanetary dust (IPD) and interstellar dust (ISD) [Mann, 2010]. I also discussed dust observations in detail at https://physics.stackexchange.com/...
Accepted

### Stellar nurseries in the "Shedding New Light on the Whirlpool Galaxy" video

Do stars tend to leave "these stellar nurseries" after a while, and it's only the short lifetime of the most massive stars that keeps them from leaving before going supernova? Yes. The lifetimes ...
• 114k

### How much matter was ejected when the Solar System formed?

It is actually the other way around: First a massive accretion disc can form, through which material looses angular momentum and accretes onto the star radially, hence being angular momentum poor. ...

### Does the Sun rotate?

Yes, Sun has differential rotation. Movement of Sun spots is one of the proofs that Sun rotates. The differential rotation causes the weird twisted magnetic fields which shows in the Sun's prominence.
Accepted

### What is the difference between LMC and SMC?

The LMC has an apparent size of about 645x550 arc mins, the SMC 320x205. Both contain several hundred million stars each. The LMC is about 14000ly in size, and is about 10 billion solar masses; the ...
• 3,204
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### What does "EW(Hα)" mean?

"EW" stands for Equivalent Width. The equivalent width of a spectral line is essentially the range of continuum one would integrate over to get the same flux as the spectral line. In your case, this ...
• 186

### If two binary brown dwarfs began to exchange gas with each other, would they both ignite into stars?

It is possible for two brown dwarfs to form a contact binary. This would not, of itself, cause core temperatures in either to rise. If the two brown dwarfs were to merge, the mass of the resulting ...
• 87.6k
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### Black Dwarf Capabilities

A 1 solar mass, Earth sized black dwarf would have a surface gravity of about 360 000 g which probably rules out manned exploration by anything we would normally think of as human. For similar reasons,...
• 9,893
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### Can a donut-shape planet or star be formed?

In principle, yes. In practice, no. The question has been studied for a long time. The classic treatment is Dyson's papers on "anchor rings" in 1893 (paper I, paper II) but it goes back to ...
• 10.2k
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### Activity of M dwarf stars

The magnetic activity is driven by a dynamo that relies on a combination of rotation and convection. M dwarfs have large convection zones or are fully convective beyond spectral type M4. They also ...
• 114k

### What will future populations of stars be like?

(Adams & Laughlin 1997) discuss the effect of increasing metallicity in the future. A higher metallicity increases the stellar burn rate since the density increases but the higher opacity reduces ...
• 10.2k