Researchers using NASA’s James Webb Space Telescope have made major progress in confirming the source of dust in early galaxies. Observations of two Type II supernovae, Supernova 2004et (SN 2004et) and Supernova 2017eaw (SN 2017eaw), revealed large amounts of dust in the ejecta of each of these objects. The matter the scientists found supports the theory that supernovae played a key role in supplying dust to the early universe.
Dust is the building block of many things in our universe – especially planets. As dust from dying stars spreads through space, it carries the basic elements that help give birth to the next generation of stars and their planets. Where the dust comes from has puzzled astronomers for decades. One significant source of cosmic dust could be supernovae – after a dying star explodes, its remaining gas expands and cools to form dust.
“Direct evidence for this phenomenon has been weak up until this point, our capabilities so far allow us to study the dust population in one relatively nearby supernova – Supernova 1987A, 170,000 light-years away from Earth,” said lead author Melissa Shahbandeh of Johns Hopkins University and Space Telescope Science Institute in Baltimore, Maryland. “When the gas cools enough to form dust, that dust is only detectable at mid-infrared wavelengths, provided you have sufficient sensitivity.”
For supernovae more distant than SN 1987A, such as SN 2004et and SN 2017eaw, both in NGC 6946 about 22 million light-years away, this combination of wavelength coverage and superior sensitivity can only be obtained with Webb’s MIRI (Mid-Infrared Instrument).
The Webb observations are the first breakthrough in the study of supernova dust production since the detection of newly formed dust in SN 1987A by the Atacama Large Millimeter/submillimeter Array (ALMA) telescope nearly a decade ago.
Another particularly interesting result of their study is not just the detection of dust, but the amount of dust detected at this early stage of a supernova’s life. In SN 2004et, scientists found more than 5,000 Earth masses of dust.
“When you look at the calculation of how much dust we see in SN 2004et in particular, it rivals the measurements in SN 1987A, and it’s only a fraction of the age,” added program leader Ori Fox of the Space Telescope Science Institute. “It is the highest dust mass detected in a supernova since SN 1987A.”
Observations have shown astronomers that young, distant galaxies are full of dust, but these galaxies are not old enough for intermediate-mass stars like the Sun to supply dust as they age. More massive, short-lived stars may have died early enough and in large enough numbers to create so much dust.
While astronomers have confirmed that supernovae produce dust, the question remains as to how much of this dust can survive the internal shocks reflected from the explosion. Seeing this much dust at this stage during the lifetime of SN 2004et and SN 2017eaw suggests that the dust can survive the shock wave – evidence that supernovae are indeed important dust factories.
The researchers also note that current mass estimates may be the tip of the iceberg. While Webb has allowed researchers to measure dust cooler than ever before, there may be undetected, cooler dust radiating even further into the electromagnetic spectrum that remains obscured by the outermost layers of dust.
The researchers stressed that the new findings are also just a hint of the Webb’s newfound research capabilities of supernovae and their dust production, and what it can tell us about the stars from which they originate.
“There is growing excitement about understanding what this dust also suggests about the core of the star that exploded,” Fox said. “After seeing these particular findings, I think our fellow researchers will be thinking about innovative ways to work with these dusty supernovae in the future.”
SN 2004et and SN2017eaw are the first of five targets included in this program. The observations were completed as part of the Webb General Observer 2666 program. The paper was published in Monthly Notices of the Royal Astronomical Society on 5 July.
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