荔枝视频

An international team of astronomers 鈥�&苍产蝉辫;including researchers from the 荔枝视频鈥�&苍产蝉辫;has uncovered two strikingly unusual 鈥渕onster鈥� black holes, revealing dramatic new clues about how galaxies are built and torn apart.

In two studies, the team examined the compact galaxy NGC 4486B in the Virgo Cluster and found that it hosts an extraordinarily massive black hole weighing roughly 360 million times the mass of the sun. Even more puzzling, the black hole is slightly offset from the galaxy鈥檚 centre 鈥� unusual, since they are typically anchored in the middle of their host galaxies.

The Virgo Cluster, about 55 million light-years from Earth, is a rich laboratory for studying galaxy evolution. With thousands of member galaxies, many actively interacting or recently disturbed, it offers a front-row seat to processes that shape galaxies over cosmic time.

The findings are published in  across three separate papers and based on observations from a Canadian-led Cycle 1 observing program using the 鈥檚 (JWST) NIRSpec instrument. Cycle 1 refers to the first year of observations on JWST, from summer 2022 to summer 2023.

A black hole kicked off centre

鈥淭he discovery of this off-centre, post-merger supermassive black hole 鈥� offers a rare opportunity to study how black hole mergers play into their growth over cosmological timescales,鈥� says Dr. , PhD, assistant professor with the  and lead author of . 鈥淐atching this one so soon after the act is also a unique opportunity to see how the mergers sculpt the innermost regions of their host galaxies.鈥�

Astronomers have long known that nearly every large galaxy hides a supermassive black hole at its centre 鈥� cosmic heavyweights millions to billions of times more massive than our sun. Even more remarkably, these black holes appear to grow in step with their host galaxies, with tight relationships between their masses, suggesting they are key drivers of galaxy evolution.

Based on the ages and internal motions of NGC 4486B, the team estimates that, while the galaxies themselves may have merged billions of years ago, their two black holes likely took much longer to fully coalesce, possibly completing their final merger only within the last 30 or so million years.

Huge monster, tiny galaxy

In another study, the team turned to one of the smallest known types of galaxies: an ultra-compact dwarf called UCD736. These are dense stellar systems that blur the line between massive star clusters and stripped-down galaxies.

Using the telescope鈥檚 spatial resolution, the researchers detected a black hole weighing about two million times the mass of the sun at the centre of UCD736. For such a small galaxy, this is astonishing. The black hole accounts for roughly eight per cent of the galaxy鈥檚 total mass from all its stars combined, far higher than the fraction of a percent seen in normal galaxies like the Milky Way.

This suggests that UCD736 was once a much larger galaxy whose outer layers were stripped away by the Virgo Cluster鈥檚 harsh dynamical environment, leaving behind its dense nucleus and central black hole. It also represents the detection of a supermassive black hole in the most compact stellar system identified to date.

鈥淭he NIRSpec instrument on JWST has given us the unique opportunity to search for supermassive black holes within smaller and fainter galaxies than was possible with ground-based telescopes,鈥� says Solveig Thompson, BSc鈥�22, MSc鈥�24, a U荔枝视频 PhD student in physics and astronomy who鈥檚 also a member of the discovery team.

Together, the two galaxies demonstrate how studying the 鈥渕onster鈥� at a galaxy鈥檚 heart can act as a cosmic time capsule, preserving clues about the violent processes that shape galaxies.

The team plans to continue investigating similar systems in the Virgo Cluster and beyond to better test models of galaxy evolution and to uncover more monsters hiding in unexpected places.

The project received financial support from the .