Because black holes are impossible to see, one of scientists’ best hopes to study them is to look for the ripples in space-time, called gravitational waves, that they are thought to create.
Gravitational waves would be distortions propagating through space and time caused by violent events such as the collision of two black holes. They were first predicted by Einstein’s general theory of relativity; however, scientists have yet to find one.
That could change when the latest version of a gravitational wave-hunting facility gets up and running. The Laser Interferometer Gravitational Wave Observatory (LIGO) is actually a pair of observatories, in Louisiana and Washington state, that began operating in 2002. Newly sensitized detectors are being added to both.
“The advanced LIGO detectors that are now being installed will see out through a substantial part of the universe,” said California Institute of Technology emeritus professor of physics Kip Thorne, a leading proponent of LIGO. “We expect to see black holes colliding at a rate of perhaps somewhere between once an hour and once a year.”
Our universe may exist inside a black hole. This may sound strange, but it could actually be the best explanation of how the universe began, and what we observe today. It’s a theory that has been explored over the past few decades by a small group of physicists including myself.
Successful as it is, there are notable unsolved questions with the standard big bang theory, which suggests that the universe began as a seemingly impossible “singularity,” an infinitely small point containing an infinitely high concentration of matter, expanding in size to what we observe today. The theory of inflation, a super-fast expansion of space proposed in recent decades, fills in many important details, such as why slight lumps in the concentration of matter in the early universe coalesced into large celestial bodies such as galaxies and clusters of galaxies.
But these theories leave major questions unresolved. For example: What started the big bang? What caused inflation to end? What is the source of the mysterious dark energy that is apparently causing the universe to speed up its expansion?
The idea that our universe is entirely contained within a black hole provides answers to these problems and many more. It eliminates the notion of physically impossible singularities in our universe. And it draws upon two central theories in physics.
The first is general relativity, the modern theory of gravity. It describes the universe at the largest scales. Any event in the universe occurs as a point in space and time, or spacetime. A massive object such as the Sun distorts or “curves” spacetime, like a bowling ball sitting on a canvas. The Sun’s gravitational dent alters the motion of Earth and the other planets orbiting it. The sun’s pull of the planets appears to us as the force of gravity.
The second is quantum mechanics, which describes the universe at the smallest scales, such as the level of the atom. However, quantum mechanics and general relativity are currently separate theories; physicists have been striving to combine the two successfully into a single theory of “quantum gravity” to adequately describe important phenomena, including the behavior of subatomic particles in black holes.
Astronomers have found the best evidence yet that the dormant gravitational monster that lies at the centre of the Milky Way — a supermassive black hole known as Sagittarius A* — recently emitted a pair of γ-ray jets.
As they feed on stars and clouds of gas that stray too close, black holes at the centres of other galaxies create bright jets that can be seen across cosmic distances. But the Milky Way’s black hole shows no signs of such activity. Now, the Fermi Gamma-ray Space Telescope has picked up some faint γ-ray signals that suggest that Sagittarius A* has not always been so tranquil. The black hole could even have been active as recently as 20,000 years ago, after gulping down a gas cloud with a mass about 100 times that of the Sun, says Douglas Finkbeiner of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
“If these features truly are γ-ray jets from Sagittarius A*, it would tell us that our Galactic supermassive black hole has not always been as feeble as we currently observe it to be,” says Fred Baganoff of the Massachusetts Institute of Technology in Cambridge. And that would solve an enduring puzzle, he notes. Sagittarius A* is growing about 1,000 times too slowly for it to have reached its current mass of about four million solar masses since the Galaxy formed about 13.2 billion years ago. “If confirmed, the existence of γ-ray jets would provide the strongest evidence to date for the existence of higher activity in the past,” he says.
Astronomers have found a black hole that behaves like one of those batting cages that automatically spits baseballs.
The stellar mass black hole ejects glowing cannon balls of plasma simultaneously in opposite directions that blaze though space at one-quarter the speed of light. That’s fast enough to travel from the sun to Earth in half an hour!
Astronomers don’t have any idea how the ultra-fast bullets are launched, but they do know that the fuel supply for these fireworks comes from a companion star to the black hole.
Material from the companion spills into an ultra hot accretion disk encircling the black hole. Something happens during this feeding process that causes the disk to grow very hot every eight months and glow fiercely in X-rays, and then subside and begin the process all over again.
The black hole and companion star, called H1742, is 28,000 light-years away near the galactic center. NASA’s High Energy Optical Observatory first saw the X-ray sputtering in the late 1970s.
Scientists may have found the smallest black hole yet by listening to its X-ray “heartbeat.”
The black hole, if it truly exists, would weigh less than three times the mass of the sun, putting it near the theoretical minimum mass required for a black hole to be stable.
The researchers can’t directly observe the black hole, but they measured a rise and fall in X-ray light coming from a binary star system in our Milky Way galaxy that they think signals the presence of a black hole.
Until now, this X-ray pattern, which is similar to a heartbeat registered on an electrocardiogram, has been seen in only one other black hole system.
NASA’s Rossi X-ray Timing Explorer (RXTE) spacecraft measured this X-ray heartbeat in a star system in the direction of the constellation Scorpius, at a distance between 16,000 and 65,000 light-years away (a light-year is the distance light travels in a single year, about 6 trillion miles (10 trillion kilometers).
Researchers think the system, officially called IGR J17091-3624, includes one normal star with a companion black hole. Mass would stream off this normal star and fall toward the black hole, forming a flattened disk around it. As friction in the disk heats the gas to millions of degrees, the disk would emit high-energy X-rays that can be seen across the galaxy.