Astronomers using the Hubble Space Telescope are now able to measure the distances to stars and other objects more accurately than ever before, it was announced yesterday by the Space Telescope Science Institute (STScI). Basically, Hubble can now make highly accurate measurements of the distances to stars 10 times farther away than it was able to before. How did astronomers accomplish this? Simply put, they fine-tuned their analysis and observations in order to make angular measurements so precise, that it would be similar to a person being able to read a license plate at the distance of the Moon. Or more specifically, measurements as fine as five-billionths of a degree in the sky. Not bad for a telescope which is now 24 years old and still going strong.
The new technique means that astronomers can now use more distant stars to use as cosmic yardsticks, for measuring interstellar distances. For example, Hubble measured the distance to a nearby bright star that belongs to a class of stars called Cepheid variables. The star is about 7,500 light-years away in the constellation Auriga. The results were so good that astronomers can now more accurately measure the distances to other Cepheids which are more far-flung.
Exposures of the star were taken every six months, when the Earth was on opposite sides of the Sun. The idea was to track extremely subtle changes in the star’s position, which Hubble was able to do to within 1/1000 the width of a single pixel in Hubble’s Wide Field Camera 3 (which has 16.8 megapixels total). A third exposure was then taken 12 months after the first one, which allowed astronomers to subtract the subtle effects of the motion of other stars in space. Other possible errors were then removed by even more exposures later on.
The distances to Cepheid variable stars are the “bottom rung” of the so-called cosmic “distance ladder.” Their brightness can even be used to gauge the size of whole observable universe. As a first step, they can then be used to calibrate distances to more distance objects such as Type Ia supernovae.
Developed by Noble Laureate Adam Riess of the Space Telescope Science Institute (STScI) and the Johns Hopkins University in Baltimore, Md., in collaboration with Stefano Casertano of STScI, the new technique is based on the already-established best method for measuring interstellar distances called parallax. Parallax uses the Earth’s orbit as the baseline of a triangle, similar to what land surveyors do. If a target star is close enough, it will appear to zigzag in the sky during the year as a reflection of Earth’s orbit about the Sun. Parallax is most reliable for stars within a few hundred light-years from Earth. But this new refinement now increases that ability ten-fold.
As a bonus, it is thought that the new measuring technique could even provide new insights into the nature of dark energy, that still not-well-understood part of the universe which is gradually pushing everything apart at an increasing rate.