Astronomers marvel at 'perfect explosion,' a spherical cosmic fireball | Tech News

Astronomers marvel at 'perfect explosion,' a spherical cosmic fireball

Researchers on Wednesday described for the first time the contours of the type of explosion, called a kilonova, that occurs when neutron stars merge.

| Updated on: Feb 16 2023, 10:13 IST
Sickening! From light to darkness, DEATH of a star is the birth of a Black Hole!
1/5 What is a Black Hole? According to NASA, a black hole is an astronomical object with a gravitational pull so strong that nothing, not even light, can escape it. A black hole’s “surface,” called its event horizon, defines the boundary where the velocity needed to escape exceeds the speed of light, which is the speed limit of the cosmos. Matter and radiation fall in, but they can’t get out. (NASA)
2/5 Classes of black holes: Two main classes of black holes have been extensively observed. Stellar-mass black holes with three to dozens of times the Sun’s mass are spread throughout our Milky Way galaxy, while supermassive monsters weighing 100,000 to billions of solar masses are found in the centers of most big galaxies, ours included. (AP)
3/5 How are black holes birthed? A stellar-mass black hole formation happens when a star with more than 20 solar masses exhausts the nuclear fuel in its core and collapses under its own weight. The collapse triggers a supernova explosion that blows off the star’s outer layers. But if the crushed core contains more than about three times the Sun’s mass, no known force can stop its collapse and the birth of of a black hole. The origin of supermassive black holes is poorly understood, but we know they exist from the very earliest days of a galaxy’s lifetime. Once born, black holes can grow by accreting matter that falls into them, including gas stripped from neighboring stars and even other black holes. (NASA)
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4/5 First image of black hole: In 2019, astronomers using the Event Horizon Telescope (EHT) — an international collaboration that networked eight ground-based radio telescopes into a single Earth-size dish — captured an image of a black hole for the first time. It appears as a dark circle silhouetted by an orbiting disk of hot, glowing matter. The supermassive black hole is located at the heart of a galaxy called M87, located about 55 million light-years away, and weighs more than 6 billion solar masses. Its event horizon extends so far it could encompass much of our solar system out to well beyond the planets. (Event Horizon Telescope Collaboration)
image caption
5/5 Studying black holes: Astronomers have been studying black holes through the various forms of light they emit for decades. Although light can’t escape a black hole’s event horizon, the enormous tidal forces in its vicinity cause nearby matter to heat up to millions of degrees and emit radio waves and X-rays. Some of the material orbiting even closer to the event horizon may be hurled out, forming jets of particles moving near the speed of light that emit radio, X-rays and gamma rays. Jets from supermassive black holes can extend hundreds of thousands of light-years into space. NASA’s Hubble, Chandra, Swift, NuSTAR, and NICER space telescopes, as well as other missions, continue to take the measure of black holes and their environments. (NASA)
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The existence of kilonova explosions was proposed in 1974 and confirmed in 2013, but what they looked like was unknown until this one was detected in 2017 and studied intensively. (REUTERS)

Astronomers have observed what might be the "perfect explosion," a colossal and utterly spherical blast triggered by the merger of two very dense stellar remnants called neutron stars shortly before the combined entity collapsed to form a black hole.

Researchers on Wednesday described for the first time the contours of the type of explosion, called a kilonova, that occurs when neutron stars merge. The rapidly expanding fireball of luminous matter they detailed defied their expectations.

The two neutron stars, with a combined mass about 2.7 times that of our sun, had orbited each other for billions of years before colliding at high speeds and exploding. This unfolded in a galaxy called NGC 4993, about 140-150 million light years away from Earth in the direction of the constellation Hydra. A light year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).

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The existence of kilonova explosions was proposed in 1974 and confirmed in 2013, but what they looked like was unknown until this one was detected in 2017 and studied intensively.

"It is a perfect explosion in several ways. It is beautiful, both aesthetically, in the simplicity of the shape, and in its physical significance," said astrophysicist Albert Sneppen of the Cosmic Dawn Center in Copenhagen, lead author of the research published in the journal Nature.

"Aesthetically, the colors the kilonova emits quite literally look like a sun - except, of course, being a few hundred million times larger in surface area. Physically, this spherical explosion contains the extraordinary physics at the heart of this merger," Sneppen added.

The researchers had expected the explosion to perhaps look like a flattened disk - a colossal luminous cosmic pancake, possibly with a jet of material streaming out of it.

"To be honest, we are really going back to the drawing board with this," Cosmic Dawn Center astrophysicist and study co-author Darach Watson said.

"Given the extreme nature of the physical conditions - far more extreme than a nuclear explosion, for example, with densities greater than an atomic nucleus, temperatures of billions of degrees and magnetic fields strong enough to distort the shapes of atoms - there may well be fundamental physics here that we don't understand yet," Watson added.

The kilonova was studied using the European Southern Observatory's Chile-based Very Large Telescope.

The two neutron stars began their lives as massive normal stars in a two-star system called a binary. Each exploded and collapsed after running out of fuel, leaving behind a small and dense core about 12 miles (20 km) in diameter but packing more mass than the sun.

Very gradually, they drew nearer to each other, orbiting at a speedy clip. Each were stretched out and pulled apart in the final seconds before the merger because of the power of the other's gravitational field. Their inner parts collided at about 25% of the speed of light, creating the most intense magnetic fields in the universe. The explosion unleashed the luminosity of about a billion suns for a few days.

The two briefly formed a single massive neutron star that then collapsed to form a black hole, an even denser object with gravity so fierce that not even light can escape.

The outer parts of the neutron stars, meanwhile, were stretched into long streamers, with some material flung into space. During the process, the densities and temperatures were so intense that heavy elements were forged, including gold, platinum, arsenic, uranium and iodine.

The researchers offered some hypotheses to explain the spherical shape of the explosion, including energy released from the short-lived single neutron star's enormous magnetic field or the role of enigmatic particles called neutrinos.

"This is fundamentally astonishing, and an exciting challenge for any theoreticians and numerical simulations," Sneppen said. "The game is on."

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First Published Date: 16 Feb, 10:12 IST