A supermassive black hole, estimated to be around one million times the mass of the Sun, has recently made headlines by revealing its position in a dramatic fashion. This astronomical event occurred when a passing star ventured too close to the black hole, resulting in its destruction due to the immense gravitational forces at play. This catastrophic encounter released a spectacular flare of light, known as a tidal disruption event (TDE), which was captured by telescopes on Earth. Dubbed AT2024tvd, this event has shed light on intriguing characteristics of a galaxy located 600 million light-years away.
According to a team of astronomers led by Yuhan Yao from the University of California, Berkeley, the black hole responsible for AT2024tvd is not anchored to the nucleus of its host galaxy. Rather, it is classified as a wandering black hole, existing independently and not in a binary orbit with the supermassive black hole that resides at the center of the galaxy. This discovery marks the first time an offset TDE has been recorded by optical sky surveys, prompting excitement about the potential to uncover more wandering black holes in future cosmic surveys.
Yao emphasizes that this groundbreaking finding could reignite interest in studying offset tidal disruption events, as theorists have not previously focused on this phenomenon. Black holes are notoriously challenging to detect when they are alone in space, as they do not emit detectable radiation, which is our primary tool for cosmic research. While we can identify black hole pairs through gravitational waves created by their collisions, solitary black holes remain elusive.
However, there is an exception. When an object approaches a black hole closely enough, the powerful tidal forces within its gravitational field can rip the object apart, sending it spiraling beyond the event horizon. This process, known as a tidal disruption, produces a bright flare of light across the electromagnetic spectrum, allowing astronomers to study the black hole from vast distances. The event AT2024tvd was initially detected on August 25, 2024, by the Zwicky Transient Facility, a wide-field sky survey designed to identify transient phenomena such as supernovae and TDEs.
Following the initial detection, astronomers quickly employed various telescopes—radio, optical, and X-ray—to capture the event's light in detail. Yao and his colleagues traced the event back to a specific location in the sky, revealing a large galaxy 600 million light-years away. Intriguingly, their analysis identified a supermassive black hole as the source of the TDE, with a mass ranging from 100,000 to 10 million solar masses. However, the flare originated from a point outside the galaxy's center, which is unusual since supermassive black holes typically reside at the heart of galaxies.
The host galaxy of AT2024tvd already contains a supermassive black hole of approximately 100 million solar masses at its center. While some galaxies can host multiple supermassive black holes, the two in this galaxy are not gravitationally bound in a binary system. They are separated by about 2,600 light-years, with the smaller black hole moving freely within the galactic bulge.
Galaxies often acquire additional supermassive black holes when they collide with other galaxies. Over time, these black holes may find each other, leading to a binary system. The existence of a second supermassive black hole in this galaxy suggests a history of merger activity. However, it remains unclear if this wandering black hole is moving towards or away from the galactic center. It is possible that it was once part of a binary system and was ejected due to gravitational interactions or is simply on an inbound trajectory, potentially leading to a future merger.
To better understand the dynamics of these wandering black holes, researchers aim to locate more galaxies that exhibit similar configurations. Tidal disruption events like AT2024tvd present a promising avenue for illuminating the existence of massive black holes that would otherwise remain undetectable. As astronomer Ryan Chornock from UC Berkeley notes, theorists have long speculated about the existence of massive black holes located away from galactic centers, and now, with TDEs, we have a viable method to uncover them.
