Astronomers have spotted a never-before-seen type of starburst. The newly discovered cosmic explosions are around a million times less intense than similar explosions, which is why the researchers call the tiny detonations “micronovae”.
The new type of “mini” explosion is a variation on a classic nova, a powerful explosion that can occur in binary star systems – where two stars are trapped in stable orbit around each other. In these systems, the more massive partner can strip stellar material from the skin of its smaller partner. The superheated plasma stripped from the smaller star, composed mostly of hydrogen, then forms a shell of gas around the more massive star, slowly blending into the cannibal star. However, sometimes this gas can become so dense and hot that it explodes before being absorbed by the large star. The resulting explosion is very powerful and envelops the entire surface of the star, but does not destroy it. Classic novas appear as intense flashes of light, seen here Earth with advanced telescopes; these flashes can last for several weeks or even months. (Classical novae should not be confused with supernovae, which occur when stars are much more massive than the Sun collapse and fully explode.)
However, a team of astronomers recently discovered a much shorter and less intense flash from a binary star system that lasted just 10 hours before fizzled out. Following this observation, the team used the Transiting Exoplanet Survey Satellite (TESS) to spot two more similar flashes and uncovered evidence of a fourth among previous studies. Astronomers had encountered much smaller versions of classic novae, but had no way of explaining how or why.
“Initially we were very surprised,” lead researcher Simone Scaringi, an astronomer at Durham University in the UK, told Live Science. “It took us over a year after discovering these events to get a general idea of what was happening.” However, when they realized they had discovered a brand new type of stellar explosion, it was “very exciting.” , he added.
But don’t let the name fool you: micronovae still release around 22 quadrillion tons (20 trillion tons) of material in a single explosion, which according to a Explanationor about four times the mass of Earth’s atmosphere, after Britannica.
Scientists believe micronovas and classic novas only occur in binary systems in which the more massive cannibalistic star is a white dwarf — a cool, dark, and dense stellar remnant left when a sun-sized star runs out of hydrogen and helium to make up for one another to merge .
“In classic novae, the accreting white dwarf builds a layer of fresh hydrogen that covers the entire star,” said Scaringi. “Once this layer reaches sufficiently high temperatures and pressures, the entire layer ignites.” However, computer models created by the researchers have shown that hydrogen accretion during micronovae is likely to occur only around the star’s magnetic poles.
The limited accretion means that a micronova needs much less hydrogen to reach the temperature and pressure required for detonation. Because of this, the explosions are much smaller than classic novae and don’t last as long.
The study’s researchers were initially puzzled as to why accreting white dwarfs that produce micronovae collect hydrogen only at their poles. But they now suspect that such accretion is dictated by the strength of the stars. magnetic Fields.
“We believe that the white dwarf’s strong magnetic field keeps the accumulated material flux confined to the magnetic poles and prevents this flux from spreading across the entire surface of the white dwarf,” said Scaringi. It is similar to auroras (southern and northern lights) typically occur at magnetic poles on Earth because that’s where the field lines converge, he added.
The magnetic field needed to contain accretion at a star’s poles is likely to be extremely strong.
“We believe the magnetic field strength required at the surface to confine the material is on the order of 1 to 10 million gauss,” Scaringi said. For comparison, Earth’s magnetic field is between 0.25 and 0.65 gauss, which is more than a million times weaker than the strength needed to contain the mini-stellar explosions International Association for Geomagnetism and Aeronomy. The highest magnetic field strength ever measured on the sun is about 350 gauss, according to Live Science’s sister site Space.com. However, the magnetic field of most accreting white dwarfs is below the estimated threshold, which is why so many produce classic novas instead of micronovas, Scaringi added.
Despite the magnetic limitations of many accreting white dwarfs, the team suspects that micronovae are much more common than anyone thought.
“These are bright events, but they are also very fast,” said Scaringi. “If we don’t look in the right place at the right time, we’re going to miss them.” Future studies using TESS could help shed some light on how many of these new mini-explosions are actually happening and whether the same stars are producing recurring micronovae, what is likely, he added.
The new discovery also opens up the potential to learn more about it neutron stars – superdense objects the size of a city but with the mass of a star, formed when massive stars run out of fuel and collapse.
Neutron stars are known to release large amounts of energy on their surfaces from thermonuclear explosions known as Type 1 X-ray bursts. “After scaling, both micronovae and Type 1 X-ray bursts look remarkably similar,” said Scaringi. This suggests that by finding and studying more micronovae, researchers could potentially learn more about neutron stars as well, he added.
The study was published in the journal on April 20 Nature.
Originally published on Live Science.
Newly discovered ‘micronovae’ shoot out of the magnetic poles of cannibalistic stars Source link Newly discovered ‘micronovae’ shoot out of the magnetic poles of cannibalistic stars