by Astronomers have discovered a hitherto unknown source of cosmic dust. Why is this dust important to track? Well, these particles essentially act as building blocks for stars.
The international team discovered that such dust can create a type of cosmic explosion that occurs when a dead white dwarf star strips material from a companion star, then interacts with gas from its immediate environment. These events are called “Type 1a supernovae” and astronomers often call them “standard candles” because their uniform light output can be used to measure cosmic distances.
“The creation of cosmic dust is critical in astronomy,” Texas A&M University team member and astronomer Lifan Wang said in a statement. “It is connected to literally all the phenomena of the cosmos. Understanding the process by which they are formed has been one of the main objectives of many astronomical missions today.”
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This is not the first time that a supernova has been implicated in creating cosmic dust, but previous observations have been based on “core-collapsed supernovae”.
These occur when a massive star runs out of the fuel supply needed for its intrinsic nuclear fusion processes. This forces the core of the star to collapse, capturing a black hole or neutron star, while the outer layers of the star are blasted away in a supernova explosion.
However, core-collapse supernovae are not seen in elliptical galaxies that resemble major star clusters rather than organized spirals such as the Milky Way. Therefore, astronomers have struggled to explain where the dust in elliptical galaxies specifically comes from.
Wang and his colleagues have now provided an answer; this dust could be coming from a “vampire white dwarf” feeding on a cosmic companion before its top was blown off in a thermonuclear explosion.
“All life forms in the universe are cosmic dust forged in processes related to stellar evolution,” Wang said. “Our paper presents clear evidence for the condensation of a massive amount of dust particles after the explosion of a white dwarf star.”
Life after death for white dwarfs
White dwarfs are compact stellar bodies born when smaller stars run out of the fuel needed for nuclear fusion, and their cores collapse. However, those interstellar bodies do not have the mass necessary to drive a full collapse, which would eject a black hole or neutron star. Instead, they form white dwarfs.
Our own sun will undergo this process when it exhausts its core hydrogen supply in about 5 billion years. But, while our sun will die a lonely death as a cooled white dwarf, there are some white dwarfs in binary systems with companion stars that can be used to bring life back.
If these stars are close enough to each other, the white dwarf can “steal” material from the outer layers of its stellar companion. This stolen material first forms a disk around the white dwarf and, from there, inches towards the surface of the star.
This accreted material eventually accumulates, increasing the mass of the white dwarf beyond the so-called Chandrasekhar limit, equal to 1.4 times the mass of the Sun and representative of the mass limit at which a star can go supernova. . This eventually causes a thermonuclear explosion known as a Type 1a supernova.
To determine whether a Type 1a supernova could account for cosmic dust, Wang and his colleagues observed a supernova named SN 2018evt for more than three years using a combination of space-based instruments, such as NASA’s Spitzer Space Telescope and mission NEOWISE, and some ground based. observatories.
They discovered that the supernova collided with matter that had been thrown from the stars in the binary system, and they saw the white dwarf feeding on its companion before the former’s thermonuclear fate. This collision, the team observed, sends shock waves through that ejected gas, and dust forms in the gas itself as it cools after the shock waves have dissipated.
The signature of dust formation in this supernova was the decrease in optical light and its brightening in infrared light. From this, the team estimated that the collision was responsible for creating a huge amount of dust that was about 1% of the mass of the sun. And, as the gas cools further, the team believes dust production will increase 10-fold.
“The origin of cosmic dust has long been a mystery,” said Lingzhi Wang, a staff member and scientist at the South American Chinese Academy of Sciences Astronomy Center in Chile. “This research is the first detection of a significant and rapid dust formation process in a thermonuclear supernova interacting with circumstellar gas.”
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From this research, it appears that Type 1a supernovae are less efficient at producing gas than their core collapsing counterparts. This shortcoming may be offset by the fact that many Type 1a supernovae may be interacting with their environment to become a significant, or even dominant, source of dust in elliptical galaxies.
“This work provides insights into the contribution of thermonuclear supernovae to cosmic dust, and we may expect more such events in the James Webb Space Telescope era,” Wang said. “The Webb telescope sees infrared light, which is perfect. for detecting dust.”
The team’s discovery shows that white dwarfs can also play an important role in the ongoing cycle of star formation and destruction, as well as the processes that give rise to planets, and sometimes, life as we know it.
“Dust creation is simply gas getting cold enough to condense,” said Las Cumbres Observatory scientist Andy Howell. “One day, that dust will condense into planetary animals and, ultimately, planets. Creation is starting anew after stellar death. It is exciting to understand another link in the cycle of life and death of the universe .”
The research was published on Friday (February 9) in the journal Nature Astronomy.
