May 30, 2020

23.06.10- Swift Spies Black Holes Feeding on Galaxy Mergers.

NASA’s orbiting Swift telescope is in the news again, this time providing a key link between energetic nuclei and active galaxy mergers. The findings come after a survey conducted since 2004 by Swifts’ Burst Alert Telescope (BAT) of active galactic nuclei. A small percentage of these (less than 1 %) are extremely active, emitting 10 billion times the equivalent solar output. While theories have long posited that galaxy mergers feed and create galactic mass black holes, the observations carried out by Swift catch these monsters switching on in their energetic youth, and thus provide insight into their evolution. Only instruments such as BAT can penetrate the thick layers of gas and dust masking these massive black holes, which emit copious amounts of radiation in the hard x-ray spectrum. In fact, Swift has built the first ever comprehensive all sky survey in hard x-rays, with sensitivity to active galactic nuclei (AGN) 650 million light years distant. In the process, Swift has also uncovered numerous unknown AGN. The picture emerging will no doubt force scientists to rethink galaxy evolution; about 25% of the galaxies that BAT sees are potential close mergers, and 60% of those are destined to merge in the next 1 billion years or so. As we fill in the galaxy “family scrapbook,” key information will be deduced about how common (or rare) our own Milky Way galaxy is. And yes, our galaxy does harbor a galactic mass black hole of its own! And we’re also due for a collision of our own with the Andromeda galaxy in about 3 billion years, with the resulting merger tentatively dubbed Milkomeda… will whatever we evolve into, (or get replaced by) be blogging then? Imagine the views as the Andromeda closes in!