NASA’s latest Hubble telescope discovery challenges current understanding of how massive galaxies form and evolve. It is the first example of a compact but massive, flat disk-shaped galaxy that stopped making stars only a few billion years after the Big Bang . A surprising discovery, since elliptical galaxies typically contain older stars, while spiral galaxies typically contain younger blue stars.
When Hubble photographed the galaxy , astronomers expected to see a chaotic ball of stars formed through merging galaxies. Instead, they saw evidence that the stars were already born on a flat disk . It is the first observation that at least some of the early so-called “dead” galaxies, where star formation stopped , somehow evolved from a Milky Way-shaped disk to the giant elliptical galaxies we see today.
Through the phenomenon of gravitational lensing , a massive group of galaxies acts like a natural zoom lens in space, magnifying and stretching images of much more distant background galaxies. By pairing this natural lens with Hubble’s resolving power, scientists were able to see the center of the dead galaxy.
According to the researchers, at least some of these early dead disk galaxies must have undergone major changes. Not only did they change their structure, but also the movements of their stars to end up forming an elliptical galaxy.
“This new vision makes us rethink the entire cosmological context of how galaxies burn out from the beginning and evolve into local elliptical galaxies ,” in the words of Sune Toft, director of the study at the Center for Dark Cosmology at the Niels Bohr Institute of the University of Copenhagen. . “Perhaps we have ignored from the beginning the fact that the first dead galaxies could be disks .”
Why this galaxy stopped forming stars is still unknown. It may be the result of an active galactic nucleus , where energy is gushing out from a supermassive black hole. This energy would inhibit star formation by heating the gas or expelling it from the galaxy. Or, it may be the result of the cold gas flow into the galaxy being rapidly compressed and heated, preventing it from cooling into star-forming clouds at the center of the galaxy.
Image: NASA, ESA, and Z. Levy (STScI)
