Runaway Black Hole Leaves Galaxy

Investigating HE0450–2958

Astronomers have long puzzled over the curious quasar HE0450–2958. This ultra-bright object, powered by a colossal black hole, appeared to float in space without a proper home galaxy. Researchers examined if this black hole was violently kicked out from a galaxy merger.

The team studied existing observations of HE0450–2958 and a nearby ultra-luminous infrared galaxy (ULIRG). They calculated how fast a black hole would need to travel to reach its current position from the ULIRG. They also explored ways such a massive object could be ejected.

The Speed of Escape

Their calculations show the black hole would need to zoom at about 300 kilometers per second (km/s) to cover the 10 kiloparsecs [a unit of cosmic distance equal to about 3260 light-years] in 30 million years. This speed aligns with the 130 km/s difference in speed between the quasar and another nearby galaxy. The black hole itself is a titan, weighing 800 million times the mass of our Sun. It could be feeding on gas clouds or leftover material from its violent eviction.

As the authors explain:

"If the black hole accretes at the Bondi-Hoyle accretion rate, it would have to accrete from material with a density ngas ∼ 15 (η/0.1)^-1 (vbh/200km s^-1)^3 cm^-3 to produce the observed luminosity..."

Implications and Future Research

These findings suggest that a powerful cosmic slingshot, perhaps involving multiple black holes, could explain why this quasar is seemingly homeless. This idea helps scientists better understand how galaxies and their central black holes grow and merge over the universe's history. It also sheds light on potential events that future observatories, like the Laser Interferometer Space Antenna (LISA), might detect.

The study acknowledges that the exact timing of black hole mergers is still uncertain. More observations of HE0450–2958 could reveal a hidden, faint galaxy around it. Future research will explore these ejected black holes in more detail.