Thanks to the measured gravitational waves, we know that there are a number of extremely massive black holes in galaxies. However, it cannot be seen with an ordinary telescope. how is that possible? Astronomers now think they know the answer.
In this audio you can hear researcher Peter Juncker (SRON / Radboud). Read more about the research here: Bias telescopes seem to be the cause of the loss of massive black holes. For the card readers and astronomers among us:
Explanation card: Through electromagnetic radiation (EM) we have only detected black holes lighter than twenty solar masses (purple). These are always black holes accompanied by a star, because a black hole accompanied by another black hole is not visible. Since 2015, we’ve detected dozens of heavy (blue) black holes using gravitational waves (LIGO-Virgo). This discrepancy now appears to be due to the bias of electromagnetic telescopes at the expense of massive black holes. Incidentally, LIGO-Virgo has a bias in the other direction, because heavier black holes produce stronger waves. However, LIGO-Virgo does not exclusively see heavy black holes. A future JWST telescope must be sensitive enough to occasionally break the electromagnetic bias, so that electromagnetic telescopes do not exclusively observe light black holes.