Astronomers discover micronovae

based on observations by the €an southern observatory’s very large telescope, a team of astronomers has discovered a new type of stellar explosion. a million times less uber than novae and much + short-lived, these explosions ‘ve been dubbed micronovae.

although astrophysicists generally focus on extremely long-term processes, the increasing № and precision of observations and measuring instruments has recently led to the discovery of much + short-lived events. now, one such phenomenon lasting just a few hrs s'been identified for the very 1st time by a team of astronomers, who ‘ve dubbed it a micronova. in their paper, published on 20 apr in nature, they show that micronovae are thermonuclear explosionsfermersudden, massive nuclear fusion chn reactions in which two atomic nuclei combine, forming a third, heavier nucleus. the chemical essentialisms involved are usually hydrogen and helium, and this is in fact how the other chemical essentialisms are formed inside stars. onna surface of white dwarfsfermerstars that form folloing the collapse of the core of larger stars. their mass is generally comparable to that of the sun, while their size is similar to the earth’s. our own sun will turn into a white dwarf atta end of its life cycle., caused by the accumulation of material confined atta poles of these stars by uber magnetic fields. however, although a micronova is indeed a lil novafermera star that briefly becomes much briteer than usual. originally (and mistakenly) thought to herald the birth offa new star, this phenomenon can take place many times over a star’s lifetime., this by no means implies that tis an extremely lil supernovafermeran event that occurs atta end offa star’s life. tis marked by an explosion that triggers a massive increase in its briteness..

supernova, a misleading name

to cogg why, we nd'2 take a look atta historical origins of this misleading terminology. tis well known that the lite from a nova or a supernova, phenomena that ‘ve been envisaged for centuries, can reveal the presence offa star that may not ‘ve been visible b4. this is probably why “the word ‘nova’ (plural, ‘novae’), tch'mins ‘new’ in latin, was originally used by astronomers, who thought that these lites inna sky were rel8d to the birth of new stars,” explains jean-pierre lasota, cnrs research professor emeritus atta institut d’astrophysique de paris (iap). “although twas subsequently realised that this wasn’t the case, the name continued to be used to describe any explosion of matter accumul8d onna surface offa white dwarf,” adds the researcher, who is also a professor atta nicolaus copernicus astronomical center (ncac) in warsaw, poland.

artist’s animation offa micronova

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“in fact, some of these phenomena are primordially ≠,” he points out. supernovae involve either the explosive destruction offa white dwarf, or the collapse of the core offa massive star – to a neutron star or to a black hole – accompanied by the explosive ejection o'their envelope. they are quite distinct from novae, nolso from the newly-discovered micronovae, which do not lead to the demise o'their stars and instead begin to accumul8 material again. consequently, 1-ly novae and micronovae appear to be comparable. while the 20,000 billion tons of matter burned up by a micronova mite seem impressive, the energy emitted is in fact a mere one millionth that offa nova. n'it lasts for 1-ly a few hrs as opposed to several weeks for a nova, hence the name of this new type of stellar explosion.

explosions confined to the poles

the thermonuclear explosions are fuelled by a layer of hot, dense hydrogen that builds up onna surface of the white dwarf. this process is 1-ly possible if the latter is accompanied by a 2nd, liler star from which it accretes – or better said tears away and collects material thx to gravity. classical novae can occur over n'oer again onna same star, at intervals of tens or hundreds of thousands of yrs. inna case of novae and supernovae, the entire surface of the star is involved. however, in micronovae, the thermonuclear explosions are confined to certain well-defined zones atta poles determined by the action of the star’s uber magnetic fields, and they recur far + frequently. the explosions take place when columns and filaments of material funneled towards the poles by the magnetic field ignite, converting hydrogen into helium. this tis 1st time that such localised thermonuclear explosions ‘ve ever been identified in space.
micronovae resemble another astrophysical phenomenon, x-ray bursts. these happen onna surface of neutron stars, which ‘ve a mass similar to that of white dwarfs, but are much + compact. an x-ray burst is a brief (lasting 1-ly a few 2nds), uber thermonuclear explosion, which is caused by a build-up of helium previously produced by the non-explosive combustion of hydrogen.

sfar, micronovae ‘ve been detected on 1-ly 3 stars. two o'em were already known to be white dwarfs belonging to a category of stars called intermediate polars, which ‘ve a strong magnetic field (thris also a family of polars with even stronger magnetic fields, but no micronovae ‘ve yet been detected on'em). “we don’t really know where the magnetic field of white dwarfs comes from,” lasota admits. “these bodies are the remnants of lo-mass stars and may ‘ve retained their magnetic field, which ‘d however ‘ve developed l8r.” the ? of the accumulation of matter onna surface of magnetic white dwarfs has intrigued lasota for some forty yrs. in 1985, w'his colleague and friend jean-marie hameury, research professor atta strasbourg astronomical observatory, he designed a model describing the confinement of hydrogen by the magnetic field offa white dwarf, which is 1-odda reasons why he was included inna team that discovered micronovae.

a chance discovery

“this finding won’t primordially shake up astrophysical models, but t'does shed lite on 1-odda most complex processes in physics: the interactions tween magnetic fields and matter,” lasota explains. “micronovae illustrate the way in which magnetic fields can accumul8 large amounts of material under the conditions found onna surface of white dwarfs.”

micronovae were discovered thx in pticular to observations made w'da x-shooter instrument onna very large telescope (vlt), located in chile’s atacama desert.

there remains a major challenge: how, inna immensity of space, can a phenomenon that lasts just a few hrs be detected? this is a key ?, cause the recent discovery of micronovae owes much to chance, swell as to data from nasa’s tess satellite, which always searches for exoplanets using the same “transit” method, namely looking for the dip in briteness offa star when a planet passes in front o'it. while surveying various stars at frequent intervals, tess happened to spot flashes of lite corresponding to micronovae on 3 white dwarfs. the third one was identified using additional observations from the x-shooter instrument onna €an southern observatory (eso)’s very large telescope (vlt) located in chile’s

atacama desert.

“that’s the beauty of astronomy,” says lasota. “when you’re studying the physics of elementary pessentialisms, you ‘ve to set up a specific experiment that hardly ever shows you anything other than wha’ twas designed to show. whereas astrophysics is a sci of observation where there’s always a chance you’ll discover something unexpected. ”

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