Look at the sky on a clear night, and you'll see a lot of stars. Sometimes they look almost at hand or at least a short ride of rockets. But the planet closest to Earth – without counting our sun – is more than four light years away, 25 trillion miles away.
There are more than 100 billion stars in our Milky Way galaxy, and although we've learned a lot about them, there are relatively few that are measured directly because they are so far away. The size of a star is a key piece of information that opens up many other mysteries about it. Several methods were used to measure the size of the stars, but each has its limitations.
But now an international team, including researchers from the University of Delaware, has discovered a new way to determine the size of the stars. Their method draws on the unique capabilities of a highly energetic radiation imaging array array system (VERITAS) at the Fred Lawrence Wipple Observatory in Arizona – and asteroids that pass in place just at the right time.
Using the technique, the collaboration of 23 universities and research institutes, led by Tarek Hassan Medwich Electron-Synchrotron and Michael Daniel of the Smithsonian astrophysical observatory, exposed the locomotives of a giant star 2,674 light-years away, a solar star, 700 light-years away. Measured in the night sky so far. The study was published on Monday, April 15 in the journal Nature Astronomy.
"Knowing the size of a star is of overall importance," said Jamie Holder, a professor in the Department of Physics and Astronomy of the UD and co-author of the study. "How big and how a star tells you how it was born, how long it will shine, and how it will eventually die."
However, almost every star in the sky is too far to be accurately measured by even the best optical telescopes.
"You just can not solve the color like the color of a star," Holder said. "It will look blurred through your telescope."
To overcome this limitation, scientists are using an optical phenomenon called "indirect" to measure the diameter of a star. When an object passes in front of a star, an event called "occult", the shadow and the surrounding pattern of light waves can be used to calculate the size of the star.
In this pilot study, the object that passed in front of the star was an asteroid – a few fragments of space left from the world when the planets were formed about 4.6 billion years ago.
Asteroids travel at an average speed of 15 kilometers per second, which added to the challenge of the group. Typically, VERITAS telescopes watch weak bluish lips, because high-energy cosmic particles and gamma rays produce as they run through the earth's atmosphere. While the telescopes do not produce the best optical images, they are very sensitive to rapid versions of light, including stars, thanks to their huge mirrored platform, fragmented in hexagons like a fly's eye. The holder was involved in the construction and projection of the telescopes in 2006, and all the light sensor modules for the four telescopes were assembled at the UD.
PhD UD makes pioneering observations
Using four large VERITAS telescopes on 22 February 2018, the team can clearly identify the diffraction pattern of TYC star 5517-227-1 as the 60-km (37 mi) asteroid Imprinetta passed.UD doctoral student Tyler Williamson was there for observation.
"It was our first time making this kind of measurement, so we made sure to give ourselves enough time to set up the procedure exactly," said Williamson, who was one of the three scientists on duty that night. "The occult itself takes only a few seconds, but we point the telescope to the star for about 15 minutes or so to get an estimate of how it looks before and after the event. If you want to identify a shadow, you need to know how the object looks, without blocking it.
Typically, when a team takes data, a computer gives them a real-time view of what they collect as it comes. But they had no way of seeing it happen. They just had to point to the telescope and wait.
"No one was sure that the hiding would even be seen from our place in the first place," he said. "The last estimate we made at night was that there was a 50 percent chance that the shadow would be placed on our observatory – the asteroid is small, and there was uncertainty in size and orbit, so you can not say for sure where the shadow would fall."
The team took the data, e-mailed it to the project's lead researcher and called it Night.
"I remember waking up the next afternoon to the underground e-mail, with a beautiful field showing the silhouette," Williamson said. "We were all very excited, and as observers we would be very happy to be part of the result."
VERITAS telescopes allowed the crew to take 300 pictures every second. From these data, the brightness profile of the indirect pattern can be reconstructed with high precision, resulting in an angular or visible diameter of 0.125 billion stars. Together with a distance of 2,674 light-years, the scientists determined that the star's true diameter is 11 times the edge of our sun, classifying it as a red giant star.
According to Holder, this planet is about 200 million times farther away from us than the sun, but it is still good within our Milky Way Galaxy, which is 100,000 light-years across.
The researchers repeated the success three months later on May 22, 2018, when asteroid Penelope with a diameter of 88 km hid the star TYC 278-748-1 The measurements caused an angular magnitude of 0.094 billion and a real diameter of 2.17 times that of our sun – The smallest planet ever measured.
But "small" is relative. "This planet is a dwarf G, twice as big as our sun and about 700 times farther from us than our closest star," Holder said.
While the new technique provides a resolution of ten times better than the standard method astronomers used, on the basis of the Hidden Moon, and is twice as sharp as size measurements using interferometric techniques, said the staff holder is working to refine it even more.
"Asteroids pass on Earth every day," Holder said. "VERITAS is preparing to increase its observations and expand its range of observations, to build data on an entire population of stars."
University of Delaware
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