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The Hubble Makes The First Precise Distance Measurement To An Ancient Globular Star Cluster
The Astronomers are using NASA’s Hubble Space Telescope for the first time precisely measuring the distance to one of oldest objects in-universe, the collection birth of the star.
The new, refining distance yardstick which is provides an independent estimate for the age of the universe. The new measurement is helping the astronomers to improve models.
Star clusters are a crucial ingredient in stellar models stars in each grouping are at the same distance, have the same age and same chemical composition. Therefore, constitute a single stellar population to study.
The stellar assembly is a globular star cluster is called NGC 6397, which is one of the closest such groups to Earth. The new measurement sets the cluster’s distance at 7,800 light-years away, with just a 3 percent margin of error.
Until now, astronomers have estimated the distances to our galaxy’s globular clusters by comparing the luminosities and colours of stars to theoretical models, and to the lights and shades of similar stars in the solar neighbourhood. The accuracy of these estimating varies, with uncertainties between 10 percent and 20 percent.
The new measurement uses straightforward trigonometry, the same method used by surveyors, and as old as classical Greek science. Using a novel observational technique to measure extraordinarily small angles in the sky, astronomers manage to stretch Hubble’s yardstick outside the Disk milky way galaxy.
The research team was calculating NGC 6397’s age 13.4 billion-year-old. “The globular clusters so old that if their ages and distances are deducing from models by a little bit, they s to be older than the age of the universe,” says the researchers
Accurate distances to globular clusters are used stellar models to study characteristic of young Stellar Populations.
“Any model that agrees with the measurements gives you more faith in applying that model to more distant stars,” Brown said. “The nearby star clusters serve as anchors for the stellar models. Until now, we only had accurate distances to the much younger open clusters inside our galaxy because they are closer to Earth.”
By contrast, about 150 globular clusters orbit outside of our galaxy’s comparatively younger starry disk. These spherical, densely packed swarms of hundreds of thousands of stars are the first homesteaders of the Milky Way.
Hubble astronomers are using trigonometric parallax to nail down the cluster’s distance. This technique measures the tiny, apparent shift of an object’s position due to a change in observer’s point of view. Hubble measure the evident little wobble of the cluster stars due to Earth’s motion around the Sun.
To get the exact distance to NGC 6397, Brown’s team employing an ingenious method developing astronomers. Accurately measuring distances to pulsating stars called Cepheid variables. These pulsating stars serve as reliable distance markers for astronomers to calculate an accurate expansion rate of the universe.
With this technique, called “spatial scanning,” Hubble’s Wide Field Camera 3 gauged the parallax of 40 NGC 6397 cluster stars, making measurements every six months for two years.
Researchers are then combining the results to obtain the precise distance measurement. “Because we are looking at a bunch of stars, we can get a better measurement than simply looking at individual Cepheid variable stars,” team member Casertano says.
The tiny wobbles of these cluster stars are only 1/100th of a pixel in telescope’s camera, measuring to a precision of 1/3000th of a pixel. It is the equivalent to measuring the size of an automobile tire on the moon to an accuracy 1 inch
The researchers say to reach an accuracy of 1 percent combining Hubble distance measurement of NGC 6397 which is obtaining from European Space Agency’s Gaia space observatory, which is measuring the positions and distances of stars.
The data release of the second batch of stars in the survey is in late April. “Getting to 1 percent accuracy will nail this distance measurement forever,” Brown says.
The team’s results appeared in the year of March 20th, 2018, issue of The Astrophysical Journal Letters.
The research team consists of T. Brown, S. Casertano, and D. Soderblom (STScI); J. Strader (MSU); A. Riess and J. Kalirai (STScI, JHU); D. Vandenberg (UVic); and R. Salinas (Gemini).
Hubble Space Telescope project international cooperation between NASA and ESA. NASA’s Goddard Space Flight Centre to managing telescope. Space Telescope Science Institute in Baltimore, Maryland, conducts Hubble science operations.
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