This bright image from the NASA/ESA Hubble Space Telescope shows Z 229-15, a celestial object located about 390 million light-years from Earth in the constellation Lyra. Z 229-15 is one of those interesting celestial objects that is defined as many different things: sometimes an active galactic nucleus (an AGN). sometimes as a quasar and sometimes as a Seyfert galaxy.

Which one is really Z 229-15

The answer is that it is all of these things at the same time, because these three definitions have considerable overlap.

An AGN is a small region at the heart of some galaxies (called active galaxies), much brighter than just the stars in the galaxy would be. The extra brightness is due to the presence of a supermassive black hole at the core of the galaxy. Material sucked into a black hole does not fall directly into it, but is instead drawn into a swirling disk, from where it is pulled toward the black hole. This disk of matter becomes so hot that it releases a large amount of energy across the electromagnetic spectrum, and this is what makes AGNs appear so bright.

Quasars are a particular type of AGN, usually extremely bright and quite far from Earth – hundreds of millions of light-years is considered close for a quasar, making Z 229-15 positively local. Often an AGN is so bright that the rest of the galaxy cannot be seen. Seyfert galaxies, however, are active galaxies that host very bright AGNs (quasars). Thus, Z 229-15 is a Seyfert galaxy containing a quasar, and which, by definition, hosts an AGN. Sorting in astronomy can be a challenge!