Cosmic dust comes from supernovae
Cosmic dust containing elements like iron, carbon or oxygen plays an important role in the formation of planets and stars. But early galaxies consisted only of gas, and the dust appeared later. Where the dust came from has long been a mystery.
After years of searching, astronomers have observed cosmic dust that appears to have survived the hot aftermath of a supernova. The finding was reported in the journal Science.
“When a supernova explodes, it forms a bunch of dust” said Ryan Lau, an astronomer at Cornell University and lead author of the new study. “But dust is pretty fragile material. So the question is, who’s to say the dust survives this extremely hot, violent environment? And if it does, how much?”
Using infrared images from an observatory aboard a Boeing 747, Lau and his colleagues located a supernova remnant near the center of the Milky Way with substantial amounts of cosmic dust.
“Were seeing a 10,000-year-old supernova, the oldest supernova found with dust inside it,” he said. According to the researchers’ measurements, “about seven to 20 per cent of the dust mass initially formed survived.”
The findings suggest not only that cosmic dust in the earliest galaxies could have been formed from supernovae, but that more of the dust survived than many experts had expected.
Ask well: Whiter teeth
What is the healthiest and most effective way to whiten your teeth?
There is no shortage of ways to treat tooth discoloration: strips, rinses, brush-on gels and toothpastes sold at pharmacies; bleaching treatments at the dentist; trays bought at the dentist’s office for home use.
All of these methods work, but some require patience, and others a tolerance for painful sensitivity. And the results will be only temporary.
Higher concentrations of hydrogen peroxide, a bleaching agent used in many whiteners, can be delivered in a dentist’s office, so those procedures tend to be quicker than drugstore aids.
But tooth sensitivity and gum irritation can occur, and the higher the concentration of peroxide, the more severe these side effects are likely to be.
More aggressive treatment isn’t necessarily more effective, either. A randomised trial of 90 patients found that use of a home bleaching tray with a 10 per cent carbamide peroxide gel for two weeks offered the same degree of whitening as two in-office sessions using 35 per cent hydrogen peroxide with light, which some dentists use because it supposedly activates bleaching agents.
Some dentists also use heat or lasers to activate bleaching agents. But a 2007 systematic review of evidence in the journal Dental Materials found no added benefit from heat, light or lasers, and suggested these methods “may have an adverse effect on pulpal tissue,” the soft material in a tooth’s centre. If the pulp is damaged, it may require a root canal.
Heat and hot lights can also have a dehydrating effect on teeth that makes them look whiter. It can take weeks for the teeth to rehydrate and darken slightly.
Dr. Ronald D. Perry, the director of the Gavel Centre for Restorative Research at Tufts University School of Dental Medicine, said that overall, “the light doesn’t really do anything, but the marketing behind it is so powerful.”
Before any bleaching, even when it is done at home, a dentist should check fillings and crowns, because, Perry said, applying peroxide to a restoration that is no longer perfectly sealed will be very sensitive.
In a 2014 review of tooth whitening studies, Clifton Carey, a professor at the University of Colorado School of Dental Medicine, warned that fillings designed to match a tooth’s color might become more yellow even after the use of drugstore whiteners. Or, if a tooth gets whiter and a filling doesn’t, it might stand out.
New York Times Service
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