A Star has Been Obliterated by a Roaming Supermassive Black hole

In 2024, a system designed to detect sudden brightening events discovered something strange. However, the automated system meant to identify the object couldn’t determine what it was observing. Nearly a year later, we know it was the first tidal disruption event—where a star is torn apart by a supermassive black hole—seen in visible light. Unusually, the black hole isn’t at its galaxy’s center. Instead, an even more massive object resides there, actively consuming matter at the same time.

The object, now called AT2024tvd, was found by the Zwicky Transient Facility, which scans the northern sky every two days. Its software detects sudden changes in brightness, including tidal disruption events where a star is torn apart by a supermassive black hole.

Unusual Location of AT2024tvd Defies Typical Tidal Disruption Event Patterns

Typically, supermassive black holes are found at the center of galaxies. As a result, the scanning software only identifies something as a potential tidal disruption event if it matches a previous light source at the same location. This wasn’t the case with AT2024tvd, which seemed to be more than 2,500 light-years away from the galaxy’s center. Because of this, the software didn’t flag it as a possible tidal disruption event, and it wasn’t until further investigation that people realized what it actually was.

Luckily, researchers were able to arrange follow-up observations across a range of wavelengths, from x-rays to radio waves. The Hubble Space Telescope and the Very Large Array both resolved the brightened object (AT2024tvd) and a bright spot at the galaxy’s center, likely the central supermassive black hole. The brightness of this spot suggests that the black hole is currently consuming matter.

Observational Evidence Confirms AT2024tvd as a Tidal Disruption Event

All the observations confirmed that AT2024tvd is a tidal disruption event. For instance, it maintained a high temperature throughout the observations, unlike a supernova, which typically cools over time. Additionally, there were fewer high-energy X-rays than expected from a supernova. The UV spectrum matched other tidal disruption events, showing elements like carbon and nitrogen that don’t require a supernova to form.

This makes it the fourth tidal disruption event linked to a supermassive black hole not situated at the galaxy’s center, and the first to be initially identified at visible wavelengths.

This brings up two questions: why are there two supermassive black holes here, and why is one located away from the center of the galaxy? The first question is fairly straightforward to answer. It seems that large galaxies form through galaxy mergers, where multiple smaller galaxies combine. Each of these smaller galaxies would have its own black hole. Usually, new supermassive black holes drift to the galaxy’s center and merge with the central one.

The Gradual Process of Black Hole Mergers in Large Galaxies

However, it’s important to note the phrasing: “in most cases” and “eventually.” Even when a merger does occur, the process is gradual, potentially taking millions or even billions of years. As a result, a large galaxy could have as many as 100 extremely massive black holes roaming within it, with around 10 of them having masses over 1 million times that of the Sun. The galaxy that AT2024tvd is located in is very large.

One consequence of these roaming black holes is that not all of them will merge. If two black holes approach the central one simultaneously, gravitational interactions could propel the smaller one at nearly the velocity required to escape the galaxy entirely. As a result, these supermassive black holes could end up far from the galaxy’s center for millions of years.

At present, it’s unclear which of these scenarios explains AT2024tvd’s location. The galaxy it resides in doesn’t appear to have undergone a recent merger, but it’s possible that it could be a remnant from an ancient merger.

It’s worth noting that all the galaxies where we’ve observed off-center tidal disruption events are very large. The study on AT2024tvd suggests larger galaxies, with more past mergers, have more scattered supermassive black holes. The researchers also propose that off-center events will be the only ones we observe in large galaxies. This is because larger galaxies house larger supermassive black holes at their centers. When a black hole is massive enough, its large event horizon lets stars fall in intact, releasing all energy inside.

If you were close enough to witness this, the star would likely simply vanish from view.

Read the original article on: arstechnica

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