TheNASA Hubble Space Telescopehas captured a new image of the spiral galaxy known asESO 498-G5, about 100 million light-years away in the constellation Pyxis (The Compass). An interesting feature of this galaxy is that its spiral arms reach all the way to the center itself, so the core of ESO 498-G5 looks a bit like a miniature spiral galaxy. This type of structure contrasts with the star-filled elliptical centers present in many other spiral galaxies, which appear as incandescent masses.
Astronomers refer to the characteristic spiral-shaped bulge of galaxies similar to ESO 498-G5 as disk-shaped bulges, while the centers of the bright ellipticals are known as classical bulges. Observations by Hubble, which does not suffer from the distorting effects of Earth’s atmosphere, have helpedreveal the existence of these two different types of galactic centerss.
Star formation is still ongoing in the disc-shaped centers, while it has ceased in the classical bulbs. This implies that galaxies can be similar to Russian matryoshka dolls: classic bulbs look a lot like a miniature version of an elliptical galaxy, embedded in the center of one spiral, while disk-shaped ones seem to stick out of a second one. smaller spiral galaxy located at the heart of the first. Namely:a spiral within a spiral.
The similarities between the types of centers of galaxies and the galaxies themselves go beyond their appearance. Like giant elliptical galaxies, those with classical bulges consist of large swarms of stars that move around in random orbits. Rather, the structure and motion of stars within disk-shaped centers reflects the spiral arms arranged in the disk of the galaxy.
These differences suggest different origins of the two types of centers: while those of classical bulges are believed to arise from events such as mergers with other galaxies, those of disc-shaped bulges have evolved little by little, and the development of their spiral pattern causes stars and gas to migrate toward the center of the galaxy.
