Skip to main content

This galaxy helps astronomers measure the size of the universe

Trying to measure the size of the universe is no easy task. We know that the universe is expanding, though the exact rate of this expansion is not yet fixed. So one method that astronomers use to tell how far away very distant objects are is called the cosmic distance ladder. The idea is that different objects can be used as rungs on a ladder for measuring different distances, from looking at the movements of stars to observing pulsating stars called cepheid variables to observing a type of supernova called a Type Ia.

Each of these classes of objects is useful for determining increasingly large distances, but they need to be calibrated to each other to be accurate. Cepheid variables change in brightness over time, and importantly, the speed of the changes in brightness is correlated to their true brightness (as opposed to how bright they appear in the sky). So when we see a star pulsing we can work out its true brightness, and by comparing this to its apparent brightness, we can work out how far away it is.

The NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 imaged this lonely spiral galaxy called UGC 9391. The galaxy resides 130 million light-years from Earth in the constellation Draco near the north celestial pole. Its star-studded spiral arms stand in splendid isolation against a backdrop of distant galaxies, which are only visible as indistinct swirls or smudges thanks to their vast distances from Earth.
The NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 imaged this lonely spiral galaxy called UGC 9391. ESA/Hubble & NASA, A. Riess et al

For even more distant objects, we can use Type Ia supernovae as yardsticks, because these explosions always have approximately the same level of brightness — so once again, we can compare the apparent brightness to the true brightness to work out how far away they are. But, to measure distance accurately, we need a way to check that distances calculated based on cepheids are calibrated to distances based on supernovae.

That’s where galaxies like UGC 9391 come in, which both contains cepheid variable stars and recently hosted a Type Ia supernova. This week’s image from the Hubble Space Telescope shows this handy distance-measuring tool in all its glory.

“UGC 9391 helped astronomers improve their distance estimates by providing a natural laboratory in which to compare two measuring techniques – supernova explosions and Cepheid variables,” Hubble scientists explained. “Improving the precision of distance measurements helps astronomers quantify how quickly the universe is expanding – one of Hubble’s key science goals.”

Editors' Recommendations

Georgina Torbet
Georgina is the Digital Trends space writer, covering human space exploration, planetary science, and cosmology. She…
James Webb spots clues to the large-scale structure of the universe
An arrangement of 10 distant galaxies marked by eight white circles in a diagonal, thread-like line.

If you look at the universe on a big enough scale, the billions of galaxies out there aren't randomly scattered. Instead, they form a structure made up of galaxies and the gas between them, which are connected into filaments in a geometric-like pattern. This structure is known as the cosmic web, and it was created by the conditions at the start of the observable universe during the Big Bang.

The James Webb Space Telescope recently spotted some of the earliest evidence of this web, identifying some extremely old galaxies which were observed just 830 million years after the Big Bang and which are formed into a filament.

Read more
Hubble image of the week shows an unusual jellyfish galaxy
The jellyfish galaxy JO206 trails across this image from the NASA/ESA Hubble Space Telescope, showcasing a colorful star-forming disk surrounded by a pale, luminous cloud of dust. A handful of foreground bright stars with crisscross diffraction spikes stands out against an inky black backdrop at the bottom of the image. JO206 lies over 700 million light-years from Earth in the constellation Aquarius.

This week's image from the Hubble Space Telescope shows an unusual type of galaxy named for its aquatic look-alike: a jellyfish.

The jellyfish galaxy JO206 is shown below in an image taken using Hubble's Wide Field Camera 3 instrument. Located 700 million light-years away, in the constellation of Aquarius, this image of the galaxy shows both the bright center of the galaxy and its long tendrils reaching out toward the bottom right. It is these tendrils that give jellyfish galaxies their names, and they are formed through a process called ram pressure stripping.

Read more
Peer inside the bar of a barred spiral galaxy in new James Webb image
A delicate tracery of dust and bright star clusters threads across this image from the NASA/ESA/CSA James Webb Space Telescope. The bright tendrils of gas and stars belong to the barred spiral galaxy NGC 5068, whose bright central bar is visible in the upper left of this image. NGC 5068 lies around 17 million light-years from Earth in the constellation Virgo.

The newest image from the James Webb Space Telescope shows a stunning display of dust and stars that form the bar of the barred spiral galaxy NCG 5068, located 17 million light-years away. Like our galaxy, the Milky Way, this galaxy has a central bar that is a more concentrated region of stars and dust compared to the arms that reach out from the galaxy's center.

The image was taken using two of Webb's instruments, the Mid-Infrared Instrument (MIRI) and the Near Infrared Camera (NIRCam). By looking in both the mid- and near-infrared wavelengths, Webb is able to pick out features like the swirls of dust and gas, as well as the stars in this region, with the bar of the galaxy glowing in the top left of the image.

Read more