Have you ever looked up at the night sky and wondered why so many billions of stars illuminate what would otherwise be a chasm of impenetrable blackness?
When the Big Bang exploded into that blackness, the universe began to spread its cosmic wings at an unreal rate as it expanded and expanded, swirling with particles that cooled into an ultradense neutral hydrogen gas 400,000 years later. Early stars and galaxies struggled to shine through the murk, which is why this period is known as the cosmic dark ages.
Then there was light. Luminous, radiant, brilliant light.
Cosmologists know that the reason for the sudden light show was the result of the intergalactic medium—that shroud of neutral hydrogen—somehow heating up and going from neutral and freezing to warm and ionized. They have also theorized that these primordial stars and galaxies emitted enough intense UV radiation to burn off the hydrogen and spark the epoch of reionization that would turn the universe into a sparkling skyscape. What they still cannot be sure of is how enough UV light to make the stars shine again came into being, and from where.
The answer may be hiding in black holes.
However ironic this sounds, because black holes are usually thought of as swallowing all light and matter into oblivion, it is backed by a new Chandra X-Ray Observatory study that was recently published in Monthly Notices of the Astronomical Society. Some black holes don’t just devour, but spit out high-powered jets of energetic x-ray particles.
“As matter falls into a black hole, it starts to spin, and the rapid rotation pushes some fraction of the matter out,” said Philip Kaaret of the University of Iowa, who is also the study’s lead author. “They’re producing these strong winds that could be opening an escape route for ultraviolet light. That could be what happened with the early galaxies.”
600 million light-years from Earth, the galaxy TOL 1247-232 is one of only three galaxies somewhat close to our planet found to have ultraviolet light escaping from them. Chandra observed something waxing and waning that couldn’t possibly be a star, because no changes in brightness occur in stars, but much smaller objects, and that makes black holes pretty much the only option. What astronomers at Chandra had their telesecope trained on was no star but X-ray jets that could only have been streaming from the gaping mouth of a black hole.
“It’s possible the black hole is creating winds that help the ionizing radiation from the stars escape,” Kaaret explained. “Thus, black holes may have helped make the universe transparent.”
Ancient stars were massive and led short, brutal lives, burning out into black holes. Extremely hot material around these black holes gives birth to X-rays, and the UV radiation that joined forces with them to light up the universe is thought to have issued from blazing stars. However, there is another theory about where these X-rays could have emerged from.
“Another possible origin of the X-ray emission,” according to Kaaret and his colleagues, “is from an ultraluminous (ULX) or hyper-luminous (HLX) X-ray source. ULXs are thought to be X-ray binaries that contain stellarmass black holes or neutron stars. HLXs may be super-Eddington accretors [possibly quasars] or intermediate mass black holes."
While the mystery hasn’t been completely illuminated, Chandra’s repeat X-ray imaging of TOL 1247-232 and observations of similar galaxies, such as Haro 11, may finally shed light on the early shadows of space.