For many years the existence of medium sized Black Holes (IMBH) have eluded scientists. BH of several times the mass of our sun have been found, as well as SMBH with millions of sun masses. SMBH's and small ones mass grows with time, as matter gets transferred to the accretion disc and later gets absorbed or by merging. Quoting a paper from 2018:

Although many IMBH candidates have been identified, none are accepted as definitive; thus, their very existence is still debated.

My question is: If we know BH grow, where are the medium sized Black Holes? How come small sized ones are easier to spot than medium ones? Why is their mere existence beign debated on?

  • $\begingroup$ IMBH are uncommon because they either form via collision of two or more lesser black holes, or form via an extremely massive star via direct collapse. SMBH form through a IMBH "eating" a whole nebula in the early universe, or other unknown factors such as swallowing a star. Quasars - well, we don't know much about how they form, but they are indeed very massive SMBH. $\endgroup$ – fasterthanlight Mar 3 at 16:50
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    $\begingroup$ Is there any evidence supporting those claims about IMBH? Would you please point a paper out. And why are they so elusive compared to small ones? $\endgroup$ – Wilhelmroentgen Mar 3 at 16:54
  • $\begingroup$ See this Wiki article about it. $\endgroup$ – fasterthanlight Mar 3 at 16:59
  • $\begingroup$ Ok so there has been no confirmed IMBH. The Wiki article only talks about "potential discoveries" and "IMBH candidates" $\endgroup$ – Wilhelmroentgen Mar 3 at 17:03
  • $\begingroup$ different but related: What is the “hypothesized lower mass gap” between 2.5 and 5 solar masses? $\endgroup$ – uhoh Mar 4 at 0:26

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