The origin of the abundant stardust, floating around within the multitude of galaxies inhabiting the ancient Universe, is a mystery. For decades, however, many astronomers have suspected that stellar explosions, heralding the fiery demise of massive stars, may be the culprits! Stardust is crucial for both star birth and the formation of rocky planets like our own Earth, and it provides the ingredients for that wonderful brew called "life"--but no one has been able to definitely determine where all that crucial cosmic dust came from. In fact, observations of supernovae near our own barred-spiral Milky Way Galaxy indicate that they create too little material to account for the copious quantities of dust floating around in the early Universe. In July 2014, a team of astronomers reported that they have been able to follow stardust being churned out by supernova blasts in real-time--showing that these Cosmic dust factories produce their grains of dust in a two-step process, starting soon after the stellar blast, but also continuing for years afterwards.
The international team of astronomers used the X-shooter spectrograph on the European Southern Observatory's (ESO's) Very Large Telescope (VLT) on Cerro Paranal in Chile, to measure the amount of visible light absorbed by the dust grains, as well as the infrared radiation that the grains themselves emitted. The astronomers analyzed the light being shot out from the supernova SN2010jl as it slowly dimmed over time, observing the supernova nine times in the months following the explosion-- and for a tenth time 2.5 years after the blast. This unusually brilliant supernova, the sad result of the death of a massive star, exploded in the small galaxy UGC 5189A. The results of the new study are published online in the July 9, 2014 issue of the journal Nature.
"By combining the data from the nine early sets of observations we were able to make the first direct measurements of how the dust around a supernova absorbs the different colors of light. This allowed us to find out more about the dust than had been possible before," explained lead author Dr. Christa Gall in a July 9, 2014 ESO Press Release. Dr. Gall is of Aarhus University in Denmark.
Even though astronomers have long suspected that supernovae may be the main source of dust, especially in the young Universe, its origin in galaxies remains mysterious--it is still unclear how and where the dust grains condense and grow. It is also unclear how they manage to avoid being destroyed in the hostile environment of a star-birthing galaxy. However, the new study offers to lift this obscuring veil for the first time, documenting the formation of dust emitted from SN2010jl only a few weeks following its blast, and continuing for almost 2.5 years afterwards. The study also shows the formation of large dust grains that were able to survive the violent, harsh shocks of the supernova. It also reveals that dust production starts off slow, at first--but eventually speeds up.
Stellar Life
Stars are born in dense, cold blobs that form within enormous, frigid, dark molecular clouds that haunt our Universe like billowing phantoms. There are many such dark, cold, giant clouds floating through interstellar Space, and they serve as strange, secretive nurseries for the multitude of sparkling baby stars that set our Galaxy ablaze with their dancing light. At long last, within a dense star-forming blob, hidden within the cold flowing folds of the enormous cloud, delicate, fragile threads of material twirl around together, thus combining to create clumps that continue to increase in size for hundreds of thousands of years. The growing blob eventually acquires sufficient mass to collapse under the heavy weight of its own gravity--and a brilliant baby star is born.
The dark, giant clouds are mostly made up of frigid gas, but they also carry within them a supply of dust. These swirling, ghostlike clouds are scattered throughout our Milky Way, and they carry within their billowing folds the gas and dust of previous generations of long-dead, ancient stars. When the dense star-birthing blob is squeezed sufficiently by the crush of gravity to cause the hydrogen atoms tumbling around within it to fuse, the baby star's fire is lit, and it will continue to glare with wonderful ferocity for as long as it "lives". All of our Galaxy's billions of stars, including our Sun, were born this way.
Stars "live" out their entire main-sequence (hydrogen-burning) lives by keeping a delicate balance between two ancient rivals--gravity and radiation pressure. The radiation pressure maintained by a thriving star on the main-sequence, keeps this roiling, seething ball of searing-hot, mostly hydrogen gas, puffed up against the squeeze of gravity. The radiation pressure of a star is manufactured by way of the process of nuclear fusion, whereby hydrogen--the lightest atomic element in the Universe--is burned in the star's core to form helium, which is the second-lightest atomic element. This process, termed stellar nucleosynthesis, relentlessly fuses heavier atomic elements out of lighter ones. All of the atomic elements heavier than helium were churned out in the nuclear-fusing hearts of the multitude of stars inhabiting our Universe--or else in their supernova deaths, which manufactured the heaviest atomic elements of all, such as gold and uranium.
Origin Of Stardust
The international team of astronomers found that the formation of dust grains begins soon after the supernova blast, and continues over a long period of time. Most earlier studies observed each supernova under scrutiny for only short periods of time, and so "they did not tell us the full story of how much dust supernovas produce," Dr. Gall told the press on July 9, 2014.
The new measurements made by Dr. Gall's team show how big the dust grains are and what they are composed of. These discoveries are a step beyond other recent results that were obtained by astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA), which initially spotted the relics of a recent blast overflowing with freshly manufactured dust from the well-known supernova dubbed 1987A (SN 1987A).
To their amazement, Dr. Gall's team found that the dust grains produced by SN2010jl were gigantic by our Milky Way Galaxy's standards--measuring 1 to 4.2 micrometers across. This is approximately four times the usual width of dust grains observed between stellar systems in our own Galaxy. In addition, the team found that dust grains larger than one thousandth of a millimeter in diameter formed quickly in the dense material swirling around the doomed star. Even though this is still quite small by human standards, it is actually quite large for a grain of Cosmic dust and the surprisingly large size renders them very hearty and resistant to the destructive processes going on all around them. How tiny dust grains could manage to survive the turbulent, destructive, and violent environment found in supernovae remnants was one of the biggest open questions of the ALMA study, to which this later result has now offered an explanation--that the dust grains are larger than expected!
"Our detection of large grains soon after the supernova explosion means that there must be a fast and efficient way to create them. We really don't know exactly how this happens," noted study co-author Dr. Jens Hjorth in the July 9, 2014 ESO Press Release. Dr. Hjorth is from the Niels Bohr Institute of the University of Copenhagen in Denmark.
However, the astronomers do have a theory about where the new dust may have formed--in the material that the dying star shed out into Space before it even went supernova! As the supernova's shock wave ballooned outwards, it formed a dense, cool shell of gas--which produces just the right environment for dust grains to form and grow.
Results from the new observations suggest that in a second stage--after about several hundred days--an accelerated dust formation process takes place which involves material that had been hurled out violently from the supernova. During the early observations conducted by the team, the quantity of dust swirling around SN2010jl was relatively small, equivalent to merely one-ten-thousandth solar-masses. However, between 500 and 868 days after the stellar blast, dust production sped up to the point that the dust mass soared more than 10-fold. This speedy rate marks a definite transition to the second phase of supernova dust production. Once material rich in carbon and other debris manufactured during the stellar blast has cooled off sufficiently, it begins to coalesce into dust--thus speeding up production. Cosmic dust is primarily composed of silicate and amorphous carbon grains, which are minerals that are also abundant on our own planet. The soot from a candle is quite similar to Cosmic carbon dust, although the size of the grains in the soot are about ten or more times larger than typical grain sizes for Cosmic grains.
At day 868--the last time that Dr. Gall's team had observed the supernova--the quantity of dust had shot up to 0.04 solar masses, or 830 Earth-masses. Furthermore, if the manufacture of dust in SN2010jl continues to follow the observed trend, by about a quarter-century after the supernova blast, the total mass of dust will be approximately 50% the mass of our Sun--which is similar to the dust mass seen in other supernovae such as SN 1987A. If a large number of supernovae exploding in the ancient Universe managed to produce dust at a similar rate, it could indeed explain the great amount of dust observed in the young Universe.
"Previously astronomers have seen plenty of dust in supernova remnants left over after the explosions. But they also only found evidence for small amounts of dust actually being created in the supernova explosions. These remarkable new observations explain how this apparent contradiction can be resolved," Dr. Gall explained to the press on July 9, 2014.
Judith E. Braffman-Miller is a writer and astronomer whose articles have been published since 1981 in various newspapers, magazines, and journals. Although she has written on a variety of topics, she particularly loves writing about astronomy because it gives her the opportunity to communicate to others the many wonders of her field. Her first book, "Wisps, Ashes, and Smoke," will be published soon.
The international team of astronomers used the X-shooter spectrograph on the European Southern Observatory's (ESO's) Very Large Telescope (VLT) on Cerro Paranal in Chile, to measure the amount of visible light absorbed by the dust grains, as well as the infrared radiation that the grains themselves emitted. The astronomers analyzed the light being shot out from the supernova SN2010jl as it slowly dimmed over time, observing the supernova nine times in the months following the explosion-- and for a tenth time 2.5 years after the blast. This unusually brilliant supernova, the sad result of the death of a massive star, exploded in the small galaxy UGC 5189A. The results of the new study are published online in the July 9, 2014 issue of the journal Nature.
"By combining the data from the nine early sets of observations we were able to make the first direct measurements of how the dust around a supernova absorbs the different colors of light. This allowed us to find out more about the dust than had been possible before," explained lead author Dr. Christa Gall in a July 9, 2014 ESO Press Release. Dr. Gall is of Aarhus University in Denmark.
Even though astronomers have long suspected that supernovae may be the main source of dust, especially in the young Universe, its origin in galaxies remains mysterious--it is still unclear how and where the dust grains condense and grow. It is also unclear how they manage to avoid being destroyed in the hostile environment of a star-birthing galaxy. However, the new study offers to lift this obscuring veil for the first time, documenting the formation of dust emitted from SN2010jl only a few weeks following its blast, and continuing for almost 2.5 years afterwards. The study also shows the formation of large dust grains that were able to survive the violent, harsh shocks of the supernova. It also reveals that dust production starts off slow, at first--but eventually speeds up.
Stellar Life
The dark, giant clouds are mostly made up of frigid gas, but they also carry within them a supply of dust. These swirling, ghostlike clouds are scattered throughout our Milky Way, and they carry within their billowing folds the gas and dust of previous generations of long-dead, ancient stars. When the dense star-birthing blob is squeezed sufficiently by the crush of gravity to cause the hydrogen atoms tumbling around within it to fuse, the baby star's fire is lit, and it will continue to glare with wonderful ferocity for as long as it "lives". All of our Galaxy's billions of stars, including our Sun, were born this way.
Stars "live" out their entire main-sequence (hydrogen-burning) lives by keeping a delicate balance between two ancient rivals--gravity and radiation pressure. The radiation pressure maintained by a thriving star on the main-sequence, keeps this roiling, seething ball of searing-hot, mostly hydrogen gas, puffed up against the squeeze of gravity. The radiation pressure of a star is manufactured by way of the process of nuclear fusion, whereby hydrogen--the lightest atomic element in the Universe--is burned in the star's core to form helium, which is the second-lightest atomic element. This process, termed stellar nucleosynthesis, relentlessly fuses heavier atomic elements out of lighter ones. All of the atomic elements heavier than helium were churned out in the nuclear-fusing hearts of the multitude of stars inhabiting our Universe--or else in their supernova deaths, which manufactured the heaviest atomic elements of all, such as gold and uranium.
Origin Of Stardust
The international team of astronomers found that the formation of dust grains begins soon after the supernova blast, and continues over a long period of time. Most earlier studies observed each supernova under scrutiny for only short periods of time, and so "they did not tell us the full story of how much dust supernovas produce," Dr. Gall told the press on July 9, 2014.
The new measurements made by Dr. Gall's team show how big the dust grains are and what they are composed of. These discoveries are a step beyond other recent results that were obtained by astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA), which initially spotted the relics of a recent blast overflowing with freshly manufactured dust from the well-known supernova dubbed 1987A (SN 1987A).
To their amazement, Dr. Gall's team found that the dust grains produced by SN2010jl were gigantic by our Milky Way Galaxy's standards--measuring 1 to 4.2 micrometers across. This is approximately four times the usual width of dust grains observed between stellar systems in our own Galaxy. In addition, the team found that dust grains larger than one thousandth of a millimeter in diameter formed quickly in the dense material swirling around the doomed star. Even though this is still quite small by human standards, it is actually quite large for a grain of Cosmic dust and the surprisingly large size renders them very hearty and resistant to the destructive processes going on all around them. How tiny dust grains could manage to survive the turbulent, destructive, and violent environment found in supernovae remnants was one of the biggest open questions of the ALMA study, to which this later result has now offered an explanation--that the dust grains are larger than expected!
"Our detection of large grains soon after the supernova explosion means that there must be a fast and efficient way to create them. We really don't know exactly how this happens," noted study co-author Dr. Jens Hjorth in the July 9, 2014 ESO Press Release. Dr. Hjorth is from the Niels Bohr Institute of the University of Copenhagen in Denmark.
However, the astronomers do have a theory about where the new dust may have formed--in the material that the dying star shed out into Space before it even went supernova! As the supernova's shock wave ballooned outwards, it formed a dense, cool shell of gas--which produces just the right environment for dust grains to form and grow.
Results from the new observations suggest that in a second stage--after about several hundred days--an accelerated dust formation process takes place which involves material that had been hurled out violently from the supernova. During the early observations conducted by the team, the quantity of dust swirling around SN2010jl was relatively small, equivalent to merely one-ten-thousandth solar-masses. However, between 500 and 868 days after the stellar blast, dust production sped up to the point that the dust mass soared more than 10-fold. This speedy rate marks a definite transition to the second phase of supernova dust production. Once material rich in carbon and other debris manufactured during the stellar blast has cooled off sufficiently, it begins to coalesce into dust--thus speeding up production. Cosmic dust is primarily composed of silicate and amorphous carbon grains, which are minerals that are also abundant on our own planet. The soot from a candle is quite similar to Cosmic carbon dust, although the size of the grains in the soot are about ten or more times larger than typical grain sizes for Cosmic grains.
At day 868--the last time that Dr. Gall's team had observed the supernova--the quantity of dust had shot up to 0.04 solar masses, or 830 Earth-masses. Furthermore, if the manufacture of dust in SN2010jl continues to follow the observed trend, by about a quarter-century after the supernova blast, the total mass of dust will be approximately 50% the mass of our Sun--which is similar to the dust mass seen in other supernovae such as SN 1987A. If a large number of supernovae exploding in the ancient Universe managed to produce dust at a similar rate, it could indeed explain the great amount of dust observed in the young Universe.
"Previously astronomers have seen plenty of dust in supernova remnants left over after the explosions. But they also only found evidence for small amounts of dust actually being created in the supernova explosions. These remarkable new observations explain how this apparent contradiction can be resolved," Dr. Gall explained to the press on July 9, 2014.
Judith E. Braffman-Miller is a writer and astronomer whose articles have been published since 1981 in various newspapers, magazines, and journals. Although she has written on a variety of topics, she particularly loves writing about astronomy because it gives her the opportunity to communicate to others the many wonders of her field. Her first book, "Wisps, Ashes, and Smoke," will be published soon.
