# What is a low mass Black Hole?

Is a Low Mass Black Hole also called a Stellar Mass Black Hole? Can Low Mass BH be also called Primordial BH?

(If low mass BH are Stellar Mass BH-What is their size in terms of the mass of the sun?)

• In what context did you see the term "low mass black hole"? – Warrick Nov 26 '14 at 19:37
• I got this from this paper Low-mass black holes as the remnants of primordial black hole formation arxiv.org/abs/1211.7082 – Hari Seldon Nov 28 '14 at 9:03
• Well, in that case, the answer to your question is in the abstract. :) "Here we focus on searches for black holes with masses of 10^4-10^6 solar masses that are found at galaxy centers. We will refer to black holes in this mass range as 'low-mass' black holes, since they are at the low-mass end of supermassive black holes." But it's not standard. – Warrick Dec 1 '14 at 14:28

Don't use the term 'low-mass black hole'. It is ambiguous and not used by astrophysicists. Rather, one distinguishes between 'stellar-mass', 'supermassive' and 'intermediate-mass' black holes. The first are remnants of stellar collapse in a supernova and typically several Solar masses. The second are the beast in the cores of most massive galaxies and have masses in the range $10^{6-10}$M$_\odot$. Finally, 'intermediate black holes' are speculative black holes in the range $10^{2-4}$M$_\odot$, which are postulated to exist as an evolutionary stage for supermassive black holes, but we have no firm evidence for their existence (though many an observation is interpreted as such).

Finally, there are even more speculative primordial black holes.

• I got the term from this paper Low-mass black holes as the remnants of primordial black hole formation arxiv.org/abs/1211.7082 – Hari Seldon Nov 28 '14 at 9:01
• That paper made the term "low-mass black holes" up. Moreover, it starts from a wrong premise, namely that the formation of supermassive BHs after $10^8$ years is a problem and hence requires some drastic solutions. All ideas that BHs can simply form from the direct collapse of gas are wrong, as they violate the Eddington limit by many orders of magnitude. – Walter Nov 28 '14 at 20:49
• thank you for clearing this up! I was confused with the terminology for 'low-mass' and couldn't find it anywhere else! – Hari Seldon Nov 28 '14 at 21:12

Stellar Mass black holes are (generally) black holes which form from collapsed stars. They get their name because the mass of the black hole is in the order of the mass of stars. I don't believe they would fit your definition of "Low Mass," as they are believed to be fairly standard in size.

Primordial black holes are theoretical black holes which were believed to have been created during the early moments of the universe. My understanding is that these would be a subset of quantum black holes, which also seem to be called micro black holes.

See this related question, in which the answer covers types of blackholes.

I'm not quite sure what the lower-end masses of observed black holes are, but in theory we could say that the lowest mass of a stellar black hole is just beyond the upper limit of mass for neutron stars, as above that limit they would be collapse into a stellar black hole. This is known as the TOV limit, and is approximated to be about 1.5-3 solar masses1, so we could say that the smallest stellar black holes could have a mass of about 1.5-3 times that of the Sun.

Note however, that this doesn't mean that the Sun is nearly massive enough to become a black hole. The mass of the resultant stellar black hole is only a small portion of the original mass of the star which created it.

1 I. Bombaci (1996). "The Maximum Mass of a Neutron Star". Astronomy and Astrophysics 305: 871–877.

• Black hole volumes are frame-dependent, but they do have them. (Their surface areas are frame-independent.) – Stan Liou Nov 26 '14 at 0:49
• Would you dispute describing the volume as approaching zero. In classical definitions of volume people seem to split between defining it as zero and approaching zero. Meanwhile, using this frame it is described as being nearly infinite. – Mitch Goshorn Nov 26 '14 at 1:02
• I would dispute it; in my experience, people who say that tend to confuse the singularity of a black hole with the black hole itself. The volume isn't tending to zero except perhaps in a frame of passing by it at ultrarelativistic velocities, etc., and those limits aren't relevant here. Your link correctly says that the volume of a Schwarzschild black hole is nigh-infinite in the Schwarzschild frame, but it incorrectly implies that $\frac{4}{3}\pi r^3$ doesn't describe the volume (it does, but in a different frame). See also here. – Stan Liou Nov 26 '14 at 1:39
• Then I'll edit this portion out, and thank you for the link! (Feel free to edit in a more accurate explanation, if you would like to) – Mitch Goshorn Nov 26 '14 at 1:46
• I got the term from this paper Low-mass black holes as the remnants of primordial black hole formation arxiv.org/abs/1211.7082 – Hari Seldon Nov 28 '14 at 9:07