58 votes
Accepted

Why are the Pillars of Creation pillar-shaped?

Your option #3 is correct; the shape has little to do with the relative motion of the gas and stars. Giant molecular clouds The pillars are part of the giant molecular cloud (GMC) which is giving ...
pela's user avatar
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46 votes
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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 (...
christopherlovell's user avatar
38 votes
Accepted

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 ...
HDE 226868's user avatar
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35 votes
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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 ...
James K's user avatar
  • 122k
29 votes
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How are we observing the newly discovered "dark galaxy" J0613+52, if it has no stars and is so far away from other galaxies?

The low surface brightness survey at the GBT is looking for H(I) emission, i.e. emission from neutral hydrogen atoms (for example see O'Neil 2023). The most obvious signature they use is the 21 cm ...
ProfRob's user avatar
  • 152k
27 votes

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 ...
Anders Sandberg's user avatar
27 votes
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The star that created our sun

There is no single progenitor of the Sun. The material that makes up the Solar System (or at least the elements heavier than helium) were made in approximately a billion stars that lived and died ...
ProfRob's user avatar
  • 152k
24 votes
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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 ...
ProfRob's user avatar
  • 152k
22 votes
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Can stars form in the stellar halo?

Stars form from cold gas, not hot. Hot gas consists of fast-moving particles which cannot condense. So stars are born in the densest regions in molecular clouds where the temperature is 10–100 K, and ...
pela's user avatar
  • 38.3k
19 votes

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 ...
ProfRob's user avatar
  • 152k
19 votes
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Star formation - Is it just gas accumulation or does dust also play a role?

Dust is usually only about 1% of the mass of the gas in the typical interstellar medium, so no, it doesn't play the role you suggest. Where it does play a role is in providing infrared emissivity. In ...
ProfRob's user avatar
  • 152k
18 votes

How do stars 1 billion times the volume of our sun form and can they become black holes?

UY Scuti is a hypergiant star. The name refers to its size, not its mass. It may well have a billion(ish) times the volume of the Sun, but it is only about ten times the mass of the Sun. A supergiant/...
ProfRob's user avatar
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17 votes
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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 &...
pela's user avatar
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16 votes
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How can a brown dwarf be more massive than a star?

Yes, it has to do something with metallicity. Brown dwarf SDSS J0104+1535 $\to 0.086\rm\, M_\odot\to[Fe/H]=-2.4$ Red dwarf EBLM J0555-57Ab $\to 0.081\rm\, M_\odot\to [Fe/H]=-0.24$ There is an article ...
User123's user avatar
  • 2,879
15 votes

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 (...
pela's user avatar
  • 38.3k
13 votes

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 ...
HDE 226868's user avatar
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13 votes
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} = - ...
ProfRob's user avatar
  • 152k
13 votes

Did the Sun's light always peak in the green wavelengths?

Nice question! Sun's spectral peak wavelength is currently 483 nm which falls under the category of green. Sun's wavelength changing In it's early days, the Sun was a lot cooler than it is today. So ...
Arjun's user avatar
  • 1,256
12 votes

Did the Sun's light always peak in the green wavelengths?

No, but that's not why plants reflect green light The Sun, as well as the light of nearly all stars in the universe, had their peak wavelengths shift at some point during their life. In the case of ...
Alastor's user avatar
  • 2,659
11 votes
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Is it possible for a star cluster to be composed of main sequence stars?

The opposite is true. You should check your sources. Globular clusters do primarily consist of small main-sequence stars. Globular clusters are believed to be formed in the halo of the Galaxy at the ...
planetmaker's user avatar
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11 votes

Can stars be born giants?

It depends what you mean by "born". If by "born" you mean commence nuclear fusion of hydrogen, then all stars are "born" on the main sequence as hydrogen burning stars ...
ProfRob's user avatar
  • 152k
10 votes

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 ...
HDE 226868's user avatar
  • 36.6k
10 votes
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What kind of nebula was the Sun formed from?

Stars and the planetary systems around them form from dark and dense molecular clouds. Physically we distinguish Hot ionized gas (supernova remnants and emission nebulae) Hot neutral gas (also some ...
planetmaker's user avatar
  • 19.4k
10 votes

How do stars 1 billion times the volume of our sun form and can they become black holes?

You are confusing volume with mass. While UY Scuti is indeed five billion times the size of the Sun in terms of volume, it is only seven to ten times the size of the Sun in terms of mass. That most ...
David Hammen's user avatar
9 votes
Accepted

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 ...
ProfRob's user avatar
  • 152k
9 votes

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 ...
Anders Sandberg's user avatar
9 votes

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. ...
AtmosphericPrisonEscape's user avatar
9 votes

Could a quasi-neutron-star exist between the maximum mass of a star and the mass of a quasi-star?

You couldn't have a quasi-star with a neutron star at its core; the formation of the neutron star, unlike the collapse to a black hole, would be accompanied by a shockwave and a burst of energetic ...
antlersoft's user avatar
  • 3,455
9 votes

What kind of nebula was the Sun formed from?

Stars are formed in molecular clouds: these are gas clouds with conditions for $H_2$ to form. Molecular clouds are typically dark nebulae, but if there is a bright star near them, then they can ...
James K's user avatar
  • 122k
9 votes
Accepted

Is there a (proposed) name for Coatlicue's progenitor?

It's most likely that Coatlicue didn't have an equivalent predecessor. Please bear in mind that we aren't certain that the Sun had such a single progenitor star, but it's a very good hypothesis. Star ...
PM 2Ring's user avatar
  • 14.5k

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