Is An Elusive Intermediate Mass Black Hole Consuming a Star in This Distant Galaxy?

Are astronomers on the precipice of discovering the primary, elusive, intermediate mass black gap (IMBH)? That’s been the case for some time, as totally different researchers current proof of them. There’s a candidate IMBH within the globular cluster Omega Centauri, and there is proof that they are close to supermassive black holes in galactic facilities. Now researchers have discovered proof of an IMBH devouring a star.

X-ray emissions are one of many major ways in which astronomers detect black holes. When materials from a companion star will get drawn towards a stellar-mass black gap, the fabric is superheated in an accretion disk and emits x-rays. The identical is true for supermassive black holes (SMBH) throughout tidal disruption events. The identical is true for the hypothesized IMBHs and the brand new candidate.

The Hubble Space Telescope and the Chandra X-ray Observatory labored collectively to sense vibrant x-ray emissions from what seems to be an IMBH in a distant elliptical galaxy 450 million light-years away. The discovery is offered in new analysis titled “Multiwavelength Study of a Hyperluminous X-Ray Source near NGC 6099: A Strong IMBH Candidate,” printed in The Astrophysical Journal. The lead creator is Yi-Chi Chang from the Institute of Astronomy on the National Tsing Hua University in Taiwan.

“We report on the intriguing properties of a variable X-ray source projected at the outskirts of the elliptical galaxy NGC 6099,” the authors write. “The optical continuum can be modeled as stellar emission from a compact star cluster or an X-ray-irradiated accretion disk, consistent with the IMBH scenario.”

The supply is known as NGC 6099 HLX-1, and Chandra first detected it in 2009 when it flared brightly in x-rays. Astronomers have been monitoring it with the ESA’s XMM-Newton since then and watched as its x-ray emission various over time. Observations from a number of different telescopes spherical out the proof.

Researchers wish to discover an IMBH as a result of they may very well be the lacking hyperlink within the black gap hierarchy.

“X-ray sources with such extreme luminosity are rare outside galaxy nuclei and can serve as a key probe for identifying elusive IMBHs,” said lead author Yi-Chi Chang of the National Tsing Hua University, Hsinchu, Taiwan. “They represent a crucial missing link in black hole evolution between stellar mass and supermassive black holes.”

This panel reveals 4 totally different pictures of NGC 6099 HLX-1 from totally different observatories at totally different instances. HLX-1 is on the outskirts of the elliptical galaxy NGC 6099, about 40,000 light-years from the galaxy’s middle. The backside left picture is from Chandra and the underside proper picture is from the Canada-France Hawaii Telescope. Image Credit: Yi-Chi Chang et al 2025 ApJ 983 109

Astronomers know what tidal disruption occasion (TDE) emissions seem like, and the Chandra discovered the identical traits within the x-rays coming from NGC 6099 HLX-1. The Hubble additionally discovered proof of a small cluster of stars close to the candidate IMBH. That’s compelling proof, since uncommon clusters of stars with uncommon motions is a technique scientists confirmed the presence of the SMBH within the Milky Way’s galactic middle. The stars close to NGC 6099 HLX-1 are tightly clustered, that means there’s ample materials for the IMBH to feast on.

When a black gap feeds on a star or different matter, solely among the matter is pulled throughout the occasion horizon. The relaxation gathers in a swirling accretion disk the place it is heated up. The materials within the accretion disk reached 3 million levels F., which the researchers say is in line with a TDE. That’s scorching sufficient to emit x-rays, and people emissions reached peak brightness in 2012, three years after the IMBH was first detected, once they have been 50 to 100 instances brighter. Since then, it declined. This hyperluminous x-ray output is simply too vibrant for a stellar-mass black gap, however does match the theorized vary for an IMBH.

An artist’s picture of a black gap with an accretion disk. As a black gap attracts materials from a star, a few of it gathers in a superheated accretion disk that emits x-rays. Image Credit: NOIRLab/AURA/NSF/P. Marenfeld

“The observed properties of HLX-1 make it an unusual and intriguing source, difficult to categorize into ordinary classes of accreting compact objects,” the authors clarify of their paper. What they’re observing is also a background AGN, as a result of nature of the x-rays they’re detecting, and the authors say it is a distinct chance. “We cannot completely rule out a distant background AGN or quasar,” they write, whereas additionally explaining that the AGN rationalization is a little bit of a attain.

One puzzling factor about NGC 6099 HLX-1 is that the x-ray emissions have an optical counterpart. This blue, point-like optical supply may very well be from a star cluster that hosts the IMBH. This agrees with concept displaying that IMBHs kind in clusters. Or it may very well be coming from x-rays that strike an accretion disk and are then re-emitted as optical mild. This interpretation additionally agrees with IMBH situations. “The morphology and brightness of the optical counterpart are consistent with a source at the outskirts of NGC 6099, such as a massive star cluster or UCD (ultra-compact dwarf),” the authors write of their paper.

How the emissions change over the following few years might clarify precisely what’s taking place with HLX-1.

“If the IMBH is eating a star, how long does it take to swallow its gas? In 2009, HLX-1 was fairly bright. Then in 2012, it was about 100 times brighter. And then it went down again,” stated research co-author Roberto Soria of the Italian National Institute of Astrophysics. “So now we need to wait and see if it’s flaring multiple times, or there was a beginning, there was peak, and now it’s just going to go down all the way until it disappears.”

This illustration reveals a star being spaghettified by a black gap throughout a tidal disruption occasion. Image Credit: NASA / CXC / M. Weiss.

In their research’s conclusion, the researchers emphasize that, “The source satisfies the main selection criteria for an IMBH.” It’s the only rationalization for the observations.

“We discussed alternative interpretations and argued that an IMBH in a compact star cluster, fed by tidal stripping or tidal disruption of a low-mass star, is the simplest explanation consistent with the data at hand,” they write of their conclusion.

At first look, that does not clarify why NGC 6099 HLX-1 began out dimmer in 2009 after which brightened by 50 to 100 instances in 2012. “At first sight, the 2009 detection seems to rule out a single TDE,” the authors write.

The finest rationalization is a star on an elliptical orbit being periodically stripped of matter throughout shut approaches to the IMBH, one thing noticed in TDEs round SMBH. This rationalization additionally explains the variable x-rays from different candidate IMBH.

“One possible answer is that HLX-1 is fed by tidal stripping of a companion star on an eccentric orbit (partial tidal disruption). This is a model that has been suggested, for example, to explain the repeated X-ray outbursts in the best-known IMBH candidate ESO 243-49 HLX-1,” the authors clarify of their conclusion.

There’s one other situation that may clarify NGC 6099 HLX-1 and its dim-bright-dim luminosity sample. The preliminary rise in luminosity in 2009 may very well be from shocked fuel in an accretion stream that intersects itself. Then the height in 2012 may very well be from the disk accretion section. More observations will assist astronomers determine it out.

“Follow-up X-ray observations will be needed to determine whether the X-ray source is now steadily declining along the expected TDE track, whether and at what luminosity threshold it will switch to the low/hard state (which will constrain the BH mass), or, conversely, whether it will rise again in the future, if the feeding source has not been completely disrupted,” the researchers write.

Real solutions for NGC 6099 HLX-1, and for the query of IMBH existence, depend on extra observations. If IMBHs are an intermediate stage between stellar mass black holes and SMBH, then discovering them as they develop by accretion is vital. There’s a proportional relationship between black gap mass and the mass of the internet hosting galaxy, and discovering extra IMBH would assist strengthen that affiliation, too. If astronomers can discover extra IMBH on the outskirts of large galaxies, it might recommend that they finally fall into the galaxy, contributing to the hierarchical progress of SMBHs.

It’s doable that one thing else makes SMBH develop, apart from merging with and absorbing IMBH. Some astrophysicists recommend that SMBH develop by direct collapse in darkish matter haloes. It’s doable that there are a number of mechanisms for SMBH progress.

We endure from an remark bias, the place SMBH are extra simply detected than IMBH. It’s doable there are numerous extra IMBH and we simply wrestle to detect them. Finding extra of them will assist astronomers perceive black gap progress.

A survey of IMBH is what’s wanted. If we discover extra of them, the place they’re positioned might assist clarify black gap hierarchy and the way they develop into so large.

“So if we are lucky, we’re going to find more free-floating black holes suddenly becoming X-ray bright because of a tidal disruption event,” said co-author Soria. “If we can do a statistical study, this will tell us how many of these IMBHs there are, how often they disrupt a star, how bigger galaxies have grown by assembling smaller galaxies.”