The Hubble telescope might be almost 24 years old, but astronomers are still finding ways to improve its capabilities.
Their latest innovation has seen them find a way to measure the distances to stars up to 10,000 light-years away.
That’s ten times farther than was previously possible with the telescope.
‘This new capability is expected to yield new insight into the nature of dark energy, a mysterious component of space that is pushing the universe apart at an ever-faster rate,’ said Noble laureate Adam Riess of the Space Telescope Science Institute (STScI) in Baltimore, US.
Riess and the Johns Hopkins University in Baltimore, in collaboration with Stefano Casertano of STScI, developed the technique to extend Hubble’s sight.
This upgraded capability is made possible using something known as parallax.
This is a trigonometric technique that can be used to make reliable measures of astronomical distances.
To understand how it works, imagine Earth’s orbit and a distant star form a triangle.
Earth’s orbit forms the base of the triangle, with two imaginary lines running to the star and making the ‘point’ of the triangle.
The length of these lines, and thus the distance to the star, can be calculated by measuring the three ‘angles’ of the imaginary triangle.
This method works well for stars that are relatively close to us, those a few hundred light-years away, but for stars further away it is harder as the angles become smaller and more difficult to measure.
To extend the yardstick, astronomers have found a way to measure smaller angles more accurately using Hubble, down to five-billionths of a degree.
They tested this by getting Hubble to measure the distance to a Cepheid variable, which is a class of bright star often referred to as a ‘standard candle’ of the universe for distance measurements.
Cepheid variables are stars that vary between large, bright states and small, dense ones.
Their importance was recognised by female astronomer Henrietta Swan Leavitt in 1908, who realised that the relationship of a Cepheid variable’s changing state and its luminosity could be used to place ‘distance markers’ across the universe.
Using this principle, Hubble correctly confirmed the star in question in the constellation Auriga was 7,500 light-years away.
It did this by taking two exposures of the target star six months apart, when our planet was on opposite sides of the sun.
A very small shift in the star’s position was then measured to an accuracy of 1/1,000th of a single image pixel in Hubble’s Wide Field Camera 3, which has 16.8 megapixels (16.8 million pixels) in total.
A third exposure was then taken six months later to remove errors.
This then gave the correct distant measurement, which the astronomers knew previously.
The telescope was so accurate, in fact, that the astronomers are now planning to use Hubble to refine the ‘cosmic distance ladder,’ a ‘rung’ of measurements for the universe that uses various Cepheid variables as distance markers.
Although Hubble might be pushing a quarter of a century in age, this latest innovation proves just how useful the telescope is in our continuing studies of the cosmos.