On Sept. 14, 2015, LIGO detected gravitational waves from two merging black holes, shown here in this artist’s conception. The Fermi space telescope detected a burst of gamma rays 0.4 seconds later. New research suggests that the burst occurred because the two black holes lived and died inside a single, massive star.
Exactly 100 years ago on Nov. 25, 2015, physicist Albert Einstein, then 36, presented a fourth and final lecture to the Prussian Academy of Sciences about his new general theory of relativity. The idea not only redefined the concept of gravity, but also ended up reshaping humanity’s perspective on reality. Here’s a look at the theory in thought and action.ANALYSIS: Event Horizon Telescope Will Probe Spacetime's Mysteries
Max Planck Institute for Gravitational Physics
Einstein was famous for his thought experiments, which often played out for years in his imagination. From the gedankenexperiment, as it is known in German, Einstein grasped fundamental concepts about the physical world that could be verified by observation and experiments. One of his most famous ones began in 1907 when Einstein pondered if a person inside a windowless elevator could tell if he was in a gravitational free-fall, or if the elevator was being hauled up by a constant acceleration. Einstein decided the laws of physics must be the same in both cases. The mathematical equation he derived to explain this so-called principle of equivalence, which equated the effects of gravitation with acceleration in zero-gravity, became the basis for general relativity.NEWS: Einstein's Theory Passes Extreme Gravity Test
A total solar eclipse on May 29, 1919, gave astronomers an opportunity to verify Einstein’s general theory of relativity by proving that the sun’s gravitational field was bending the light of background stars. The effect was only observable during time when the sun’s light was dim enough for stars to become visible. British astronomer Arthur Eddington led an expedition to the island of Principe, off the West Coast of Africa, to photograph the eclipse, which lasted nearly seven minutes. The images of stars in the region around the sun proved that Einstein’s interpretation of gravity trumped the 200-year old Newtonian model, which interpreted gravity as a force between two bodies. Einstein saw gravity as warps and curves in space and time.Time Probe: Crowdsourcing Einstein's Relativity
In 1917, Einstein amended his general relativity theory to introduce what he called the “cosmological constant,” a mathematical way to counter the force of gravity on a cosmological scale and stave off the collapse of the universe, which the general relativity theory posited. At the time, astronomers believed that the Milky Way was surrounded by an infinite and static void. In 1923, Edwin Hubble and other astronomers find the first stars beyond the galaxy and by 1929 Hubble provides evidence that space is expanding. Einstein realized the cosmological constant was a blunder. Or perhaps not. In 1998, scientists made the startling discovery that the expansion of the universe is speeding up, driven by an anti-gravity force called dark energy, which in many ways acts like Einstein’s cosmological constant. Pictured here is the Hubble Space Telescope’s extreme deep field view, which contains about 5,500 galaxies. The telescope is named after Edwin Hubble.ANALYSIS: Hawking Tries to Find Black Hole's Emergency Exit
One of the first implications of the general relativity theory was the realization that if an object is compressed enough, the dimple it generates in the fabric of space and time will be too strong for even photons of light to escape. Thus, the idea of black holes was born. Though they can’t be directly observed, astronomers have found black holes of all sizes by measuring how they affect nearby stars and gas. Pictured here is an artist’s rendering of a black hole named Cygnus X-1, siphoning matter from a nearby star.ANALYSIS: Is the Wormhole in 'Interstellar' Possible?
NASA/Swinburne Astronomy Productions
Like ripples in a pond, scientists believe that gravity transmits in waves, deforming space and time across the universe. It is similar to the movement of electromagnetic radiation, which propagates in waves, except that gravitational waves are moving the fabric of space and time itself. So far, attempts to find gravitational waves, such as those caused by two black holes colliding for example, have been unsuccessful. Next week, the European Space Agency plans to launch a prototype space-based observatory called the evolved Laser Interferometer Space Antenna (eLISA) to test a technology to find gravitational waves. Pictured above is an artist's rendering of two merging galaxies rippling space and time.NEWS: Advanced LIGO Resumes Quest for Gravitational Waves
The pair of black holes the set off the first detection of gravitational waves through space may have been spawned by the death of a single, massive star.
“It’s the cosmic equivalent of a pregnant woman carrying twins,” astrophysicist Avi Loeb, with the Harvard-Smithsonian Center for Astrophysics, said in a statement.
Scientists believe that when a massive star explodes, its core collapses into a black hole, which is a region so dense with matter that not even photons of light can escape from the gravitational warping of space and time.
Scientists detected a gamma ray flash on Sept. 14, 2015, just a fraction of a second after the Laser Interferometer Gravitational-wave Observatory (LIGO) picked up the first signals of gravitational waves, caused in this case by the merger of two black holes.
Gravitational waves are similar to electromagnetic radiation, such as radio, visible, light and X-rays, except that it is space itself that is waving.
Loeb believes that that gamma ray burst may be a clue that the black holes seen by LIGO were twins, born out of the destruction of a single star.
He theorizes that if the star was spinning very fast, the core may have been stretched into a dumbbell shape, and then separated into two sections, each forming a black hole.
“In order to power both the gravitational wave event and the gamma-ray burst, the twin black holes must have been born close together, with an initial separation of order the size of the Earth, and merged within minutes. The newly formed single black hole then fed on the in-falling matter, consuming up to a sun’s worth of material every second and powering jets of matter that blasted outward to create the burst,” the Harvard-Smithsonian Center for Astrophysics said in a statement.
NASA’s Fermi Gamma-ray Space Telescope discovered the gamma burst just 0.4 seconds after the LIGO gravitational waves’ detection, the center said. Both events came from the same general area of the sky.
Europe’s INTEGRAL gamma-ray satellite was not able to confirm the detection, however.
The prospect of pairing gamma ray bursts with gravitational wave detections presents an alternative method for measuring cosmic distances, Loeb added.
“Astrophysical black holes are much simpler than other distance indicators, such as supernovae, since they are fully defined just by their mass and spin,” he said.
Loeb’s research will be published in an upcoming issue of Astrophysical Journal Letters and appears in the online archive arXiv.org.