Astronomers have discovered a previously unknown source of cosmic dust. Why is it important to detect this dust? Well, these particles actually act as building blocks for stars.
The international team found that such dust can be created by a type of cosmic explosion that occurs when a dead white dwarf star removes material from a stellar companion and then interacts with gas from its immediate environment. These events are called "Type 1a supernovas" and often called "standard candles" by astronomers because their uniform light output can be used to measure cosmic distances.
"The formation of cosmic dust is of critical importance in astronomy," team member and Texas A&M University astronomer Lifan Wang said in a statement. "It is related to literally all phenomena of the cosmos. Understanding the process by which it is created has been one of the main objectives of many modern astronomical missions."
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This isn't the first time supernovae have been linked to the creation of cosmic dust, but previous observations have revolved around "supernovae collapsing."
These happen when a massive star runs out of fuel needed for its intrinsic nuclear fusion processes. This forces the star's core to collapse, creating a black hole or neutron star, while the star's outer layers are blown away in a supernova explosion.
However, supernova collapses do not occur in elliptical galaxies, which resemble giant swarms of stars rather than organized spirals like the Milky Way. So astronomers have struggled to explain where exactly the dust in elliptical galaxies comes from.
Wang and colleagues have now provided an answer; this dust could come from "white vampire dwarfs" feeding on a cosmic companion before blowing up their buds in a thermonuclear explosion.
"All life forms in the universe are cosmic dust created in processes related to stellar evolution," says Wang. "Our paper presents clear evidence of the condensation of a huge amount of dust particles after the explosion of a white dwarf star."
Life after death for white dwarfs
White dwarfs are dense stellar corpses that form when smaller stars run out of fuel needed for nuclear fusion, and their cores collapse. However, these small stellar bodies lack the mass needed to cause a complete collapse, which would create a black hole or neutron star. Instead, they form white dwarfs.
Our own sun will undergo this process when the hydrogen supply in its core is depleted in about 5 billion years. But while our Sun will suffer a lonely death as a cooling white dwarf, some white dwarfs exist in binary systems with companion stars that they can use to come back to life.
If these stars are close enough together, the white dwarf can 'steal' material from the outer layers of its stellar companion. This stolen matter first forms a disk around the white dwarf and from there moves centimeters to the star's surface.
This accumulated matter eventually piles up, causing the white dwarf's mass to exceed what is called the Chandrasekhar limit, equal to 1.4 times the mass of the Sun and representative of the mass limit at which a star is capable of to undergo a supernova. All this eventually leads to a thermonuclear explosion called a Type 1a supernova.
Credit: NASA's Goddard Space Flight Center Conceptual Image Lab
To determine whether Type 1a supernovae could be responsible for cosmic dust, Wang and colleagues observed a supernova called SN 2018evt for more than three years using a combination of space-based instruments, such as NASA's Spitzer Space Telescope and the NEOWISE mission, and several ground-based instruments. observatories.
They found that the supernova collided with material shed from stars in the binary system, and watched the white dwarf feed on its companion before the former's thermonuclear fate. The team observed that this collision sends shock waves through that ejected gas, with dust forming in the gas itself as it cools after the shock waves pass.
The telltale feature of the dust formation in this supernova had to do with the fact that it became fainter in optical light and brighter in infrared light. From this, the team estimated that the collision was responsible for creating a huge amount of dust, equivalent to about 1% of the Sun's mass. And as the gas cools further, the team expects dust production to increase by as much as tenfold.
"The origin of cosmic dust has been a mystery for a long time," said Lingzhi Wang, team member and scientist at the Chinese Academy of Sciences South America Center for Astronomy in Chile. "This study marks the first detection of a significant and rapid dust formation process in the thermonuclear supernova interacting with circumstellar gas."
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This research shows that Type 1a supernovae are not as efficient at producing gas as their collapsing counterparts. This shortcoming may be offset by the fact that there may be enough Type 1a supernovae interacting with their environment to be a significant or even dominant source of dust in elliptical galaxies.
"This work provides insight into the contribution of thermonuclear supernovae to cosmic dust, and more such events are expected to occur in the era of the James Webb Space Telescope," Wang added. 'The Webb telescope sees infrared light, which is perfect. for the detection of dust."
The team's revelations show that white dwarfs may also play an important role in the ongoing cycle of star formation and destruction, as well as in the processes that produce planets, and sometimes life as we know it.
"The creation of dust is just gas getting cold enough to condense," says Andy Howell, a scientist at the Las Cumbres Observatory. 'One day that dust will condense into planetesimals and eventually into planets. This is a creation that begins again in the wake of star death. It's exciting to understand another link in the universe's circle of life and death.'
The research was published Friday (Feb. 9) in the journal Nature Astronomy.
