Before diving into their collision, it's worth understanding just how extreme these objects are. A black hole is a region of space where gravity is so strong that nothing, not even light can escape once it crosses the "event horizon." Black holes form when the most massive stars collapse at the end of their lives, creating a point of infinite density surrounded by this inescapable boundary.
A neutron star, meanwhile, is what forms when a slightly less massive star explodes in a supernova. The explosion is so violent that it crushes protons and electrons together into neutrons, creating matter so dense that a teaspoon would weigh about 6 billion tons on Earth. These city-sized spheres spin incredibly fast—sometimes hundreds of times per second—and have magnetic fields trillions of times stronger than Earth's.
Central neutron star at the heart of the Crab Nebula (Credit : ESA/Hubble)
Researchers at Caltech led by Caltech assistant Professor of theoretical astrophysics Elias Most, used powerful supercomputers to simulate what happens in the final moments before a collision between these two types of objects. About one second before the black hole swallows the neutron star, something remarkable occurs: the neutron star's surface cracks open, like an eggshell! The black hole's immense gravity stretches and tears the neutron star's crust, creating "starquakes" similar to earthquakes on our planet. When the surface cracks, the neutron star's magnetic field—which can be billions of times stronger than Earth's—gets violently shaken. This creates ripples called Alfvén waves that eventually produce a burst of radio signals that future telescopes might detect.
As the neutron star gets closer to the black hole, even more extreme physics takes over. When the neutron star finally plunges into the black hole, it creates what scientists call "monster shock waves,” the most powerful shock waves predicted in the universe. These are like cosmic tsunamis, starting small but growing into incredibly violent bursts of energy.
Perhaps most surprisingly, the simulations revealed something never seen before: the birth of a black hole pulsar. When the black hole consumes the neutron star, it also absorbs the neutron star's powerful magnetic field. But black holes don't want this magnetic baggage, so they essentially fling it around as they spin, creating magnetic winds that sweep through space like a lighthouse beam. This creates a brief cosmic lighthouse that lasts less than a second, emitting bursts of X-rays and gamma rays before going dark forever.
These simulations help astronomers know what to look for when scanning the skies. While we've detected gravitational waves from black hole collisions using instruments like LIGO (Laser Interferometer Gravitational-wave Observatory), we haven't yet seen the light shows that might accompany neutron star-black hole mergers. The research suggests that these cosmic crashes might produce detectable radio signals both when the neutron star cracks and when the monster shock waves form. Future telescopes, including Caltech's planned array of 2,000 radio dishes in Nevada, might be able to catch these brief cosmic screams.
The Livingston Observatory of LIGO (Credit : Caltech/MIT/LIGO)
Scientists are now working to detect these mergers up to a minute before they happen using gravitational wave detectors. This would give astronomers precious time to point their telescopes at the right spot in the sky to catch the light show that accompanies these cosmic catastrophes.
Scientists are now working to detect these mergers up to a minute before they happen using gravitational wave detectors. This would give astronomers precious time to point their telescopes at the right spot in the sky to catch the light show that accompanies these cosmic catastrophes.
Source : Star Quakes and Monster Shock Waves
