Something strange is going on about 820,000 light-years from Earth.
Right in this region — which is fairly close cosmically — a small dwarf galaxy called Leo I appears to host a massively massive black hole that has been flying under the radar for years. This semi-hidden void is So gigantic, responsible for incredible amounts of gravity and with a mass 3 million times that of the sun, which you would never expect to live in such a small realm.
But alas, there it is.
It’s aptly named Leo I* — and according to an article published Monday in The Astrophysical Journal Letters, two scientists are hatching a plan to find out how this unnaturally large, hard-to-detect fissure formed.
In their study, astrophysicists Fabio Pacucci and Avi Loeb of the Harvard-Smithsonian Center for Astrophysics describe a fascinating way to analyze Leo I* so that we can dissect some of his backstory. Essentially, they believe we can understand the nature of Leo I* by studying the space around this black hole where many ancient stars seem to reside and are likely caught in the magnificent monster’s gravitational embrace.
“Old stars get really big and red — we call them red giant stars,” Pacucci said in a statement. “Red giants typically have strong winds that carry a fraction of their mass into the environment. The space around Leo I* appears to contain enough of these old stars to make it observable.”
“Observing Leo I* could be groundbreaking,” Loeb said in a statement.
This is because, in addition to its puzzling location in galaxy Leo I, Leo I* is also the second-closest supermassive black hole to Earth, after Sagittarius A* at the heart of our own Milky Way galaxy. (That’s the void scientists imaged last year in an absolutely spectacular milestone for astronomy.)
Oddly enough, Leo I* also has a similar mass to Sgr A*, despite, again, living in a disproportionately small galaxy – a thousand times less massive than Sgr A*’s abode.
“This fact,” said Loeb, “challenges everything we know about how galaxies and their central supermassive black holes co-evolve.”
The skeleton of a black hole
With such a great list of traits, you might be wondering why scientists haven’t directly observed Leo I* before?
Well, there’s a caveat of sorts about this black hole that makes it so hard to capture. But before we get into that, here’s a quick primer on the anatomy of black holes.
There are three main components to consider when thinking about black holes: the singularity, the event horizon, and the accretion disk.
To put it simply, black holes are extraordinarily dense regions of matter nestled in the fabric of space and time that exhibit equally extraordinarily strong gravity. Just one of these leviathans can take a bunch of stars, planets, space dust, moons – anything you can imagine, including light – and bring them all into a single point. That point is the singularity and is located at the center of the black hole.
Next we have the event horizon.
The event horizon represents the area around a black hole’s singularity, which you can think of as a fence beyond which light cannot escape. The event horizon is always at a certain distance from this point, the so-called Schwarzchild radius.
And finally there is the accretion disk.
The accretion disk is literally a disk-like structure further away from the singularity than the event horizon, but close enough to experience the beast’s gravity. This thing is like a swirling moat of dust, gas, and other desolate cosmic material caught in the stranglehold of the black hole.
But most importantly, the accretion disk is quite important in analyzing the deepest, darkest and supermassive black hole of our universe in the first place.
Hide in plain sight
“Black holes are very elusive objects and sometimes they like to play hide and seek with us,” Pacucci said. “Light rays can’t escape their event horizon, but the environment around them can be extremely bright — if enough material falls into their gravitational well.”
In other words, black holes that actively accrete dust and gas are easier to track.
In fact, staring at the accretion disks and event horizon limits of both SgrA* and M87* is how scientists created the world’s first fiery donut void images to begin with. But as you may have guessed, Leo I* is not one of those easily discernible, extroverted voids.
And, as Pacucci puts it, if “a black hole isn’t building mass, it doesn’t emit light and becomes impossible to find with our telescopes.”
However, if the astrophysicist duo is right that red giants around Leo I* give off enough material to be trapped in the void’s accretion disk, there may be some hope. “In our study, we suggested that a small amount of mass lost by stars wandering around the black hole could provide the accretion rate needed to observe it,” Pacucci explains. “Leo I* plays hide and seek, but he emits too much radiation to go unnoticed for long.”
The researchers also draw attention to how Leo I* appeared to exist in the first place by not observing its accretion disk, but rather nearby stars accelerating due to the black hole’s intense gravity.
And while Pacucci and Loeb don’t think we’ll get a breathtaking view of Leo I* like we’ve got from SgrA* and M87*, the team has already set aside some time at both the Chandra X-Ray Observatory and the Very Large Array Observatory. radio telescope in New Mexico to continue their idea.
“This is exciting,” Loeb said, “because science usually advances the most when the unexpected happens.”
After all, before we had a portrait of Sgr A*, its stark positioning at the heart of our galaxy was once nearly impossible to observe.
Then, against all odds, we observed it — and astronomy was forever changed.