Astronomers discover the first-ever "tilted blackhole" spinning on its side

This discovery could change how black holes form in the wake of supernovae.
Brad Bergan
A black hole tilted on its side, with a doomed partner being stripped of matter.NASA / CXC / M.Weiss

Wherever you go, you can't escape the circular motion.

And, excluding Uranus, all the planets in our solar system rotate on axes in general alignment with the Sun's. We see this throughout the universe because of how solar systems form, along with a lot of complicated fluid dynamics and physics.

In a region of space far away lies a binary system, where a colossal object in the center is misaligned with its partner satellite. If that seems a little odd, gets weirder: This celestial object is a black hole, pushed somehow onto its side, according to a new study published in the journal Science.

Something tipped over a black hole. And it's changing our theories.

When the Sun came into being, it formed out of the same cloud of gas that eventually condensed into the planets. Everything in the universe rotates on an axis, including our sun and the wider solar system. This spinning creates a giant protoplanetary disk of gas and dust that eventually condensed into the planets themselves. Finally, here we are, on a planet spinning on an axis, as that axis revolves around the sun, which, in turn, spins on its own axis.

It's no wonder that for thousands of years, philosophers thought that circular motion was a sign of some higher, divine being — since it's such an abundant phenomenon.

Way out in an unspeakably distant binary system called MAXI J1820+070, there is a stellar-mass (close to the Sun's mass) black hole whose axis is 40 degrees off compared to its neighbor. But even more intriguing is the question its very existence raises: what in the universe can tip over a black hole?

The black hole's incredibly fast X-ray jets ebb and flow

"The expectation of alignment, to a large degree, does not hold for the bizarre objects such as black hole X-ray binaries," said Professor Poutanen of astronomy at the University of Turku, who was lead author of the recent study, in a press release.

Of course, this isn't the first time astronomers have set sights on MAXI J1820+070. Roughly 10,000 light-years away, the black hole and its star is a binary pair where the black hole's gravity is so strong that it rips material from the host star away, creating a gigantic, X-ray-emitting disk.

Some of this extremely hot gas moving in the disk spinning around the black hole will eventually move through the event horizon — where no light can return — while other portions of the gas are fired back into space in two massive beams of deathly hot and highly radioactive jets that gush out, following the black hole's magnetic field lines.

While these jets can flow at 80 percent of lightspeed, they aren't always steady. This is why, by monitoring the beams' active and less active phases, the researchers of the recent study discovered the rotational axis of the black hole.

The black hole's tilted axis adds complexity to the idea of how new black holes warp space-time

The object was initially discovered by the MAXI instrument, aboard the International Space Station. While active at the time, the jets have since subsided in intensity as lower quantities of "fuel" material were stripped from the star and sucked into the black hole.

This changed the light profile of the weird system, where the host star became the primary source of light. And this allowed Poutanen and his fellow researchers to analyze the orbital inclination via spectroscopy.

"To determine the 3D orientation of the orbit, one additionally needs to know the position angle of the system on the sky, meaning how the system is turned with respect to the direction to the north on the sky," Poutanen says. "This was measured using polarimetric techniques."

Several different models exist for describing the way black holes form, in addition to binary systems like MAXI J1820+070. But a misalignment of 40 degrees was not easy to explain, and could change what we know about how supernovas give birth to black holes.

"The large degree of misalignment puts strong constraints on the supernova explosion and black hole formation mechanisms, as it can only decrease during the accretion stage," say the researchers.

Increasing complexity — This simply wasn't expected — especially since current models of how space-time curves around the gravitational force of a black hole are already very complex.

But "the new findings force us to add a new dimension to them," says Poutanen.

Study Abstract:

The observational signatures of black holes in x-ray binary systems depend on their masses, spins, accretion rate, and the misalignment angle between the black hole spin and the orbital angular momentum. We present optical polarimetric observations of the black hole x-ray binary MAXI J1820+070, from which we constrain the position angle of the binary orbital. Combining this with previous determinations of the relativistic jet orientation, which traces the black hole spin, and the inclination of the orbit, we determine a lower limit of 40° on the spin-orbit misalignment angle. The misalignment must originate from either the binary evolution or black hole formation stages. If other x-ray binaries have similarly large misalignments, these would bias measurements of black hole masses and spins from x-ray observations.
 
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