Another sign of the presence of a black hole is random variation of emitted X-rays.

另一种黑洞存在的标志是x射线辐射的随机变化。

youdao

One telltale sign is that black holes are often marked by a compact cluster of stars that surround them, which were pulled from the dwarf galaxy when the black hole escaped.

有证据说明，黑洞的明显标志就是它的周围经常有一群密集的恒星，这是因为黑洞从银河系逃脱的时候所造成的。

youdao

For the past few decades, though, that black hole has lain dormant, without giving much sign it was there.

FORBES: Scientists Catch A Black Hole Munching On A Giant Planet