NASAさんのインスタグラム写真 - (NASAInstagram)「This cosmic object has a lot going on. It's sometimes classified as an active galactic nucleus (AGN), sometimes as a quasar, and sometimes as a Seyfert galaxy. So what is it? The answer: it is all of these things — all at once. For starters, an AGN is a small area in the center of some galaxies that is far brighter than the galaxy’s stars alone. The brightness is caused by a supermassive black hole heating matter that falls into it. Quasars are a type of AGN. Typically they're both extremely bright and distant from Earth, but this one is "only" several hundred million light-years away. By astronomical standards, this quasar is a local. Still with us? Ok. Lastly, an AGN is so bright that the rest of the galaxy cannot be seen. But Seyfert galaxies host extremely bright AGNs that can still make the rest of the galaxy observable. To recap: this image is of a Seyfert galaxy that contains a quasar, which hosts an AGN. Any questions? Image description: At the center of the image a Seyfert galaxy containing a quasar and active galactic nucleus is visible in bright dusty shades of blue, green, and yellow, swirling around a center point. At the very center of the galaxy, its galactic core shines especially brightly painting the rest of the galaxy in light. To the right of the image, a separate galaxy shines brightly. The darkness of space envelopes the entirety of the background of this image interrupted by a sprinkling of distant galaxies. Credit: ESA/Hubble & NASA, A. Barth, R. Mushotzky #NASA #Space #Hubble #Astrophotography #Stars #Quasar #Galaxy」4月14日 2時21分