Challenges to Galactic Growth Models, or What Came First: The Black Hole or the Galaxy?
Every galaxy seems to harbor a supermassive black hole (SMBH) at the center. This engine of destruction is thought to grow with galaxies containing a central bulge, for the majority of them seem to be 3-5% of the mass of their residency. It is through mergers of galaxies that SMBH grow along with material from the host galaxy. However, some recent finding have cast this long-held view into question, and the answers only seem to lead to even more questions…
A Mini-SMBH from Beyond
Spiral galaxy NGC 4178, located 55 million light years away, does not contain a central bulge, which means it shouldn’t have a central SMBH, and yet one was found. Data from the Chandra X-Ray Telescope, Spitzer Space Telescope, and the Very Large Array place the SMBH at the lowest end of the possible mass spectrum for SMBHs, with a total a little less than 200,000 suns. Along with 4178, four other galaxies with similar conditions have been found including NGC 4561 and NGC 4395. This could imply that SMBH form under other or perhaps even different circumstances than previously thought (Chandra “Revealing”).
A Giant SMBH from the Past
Now here we have a nearly polar opposite case: one of the largest SMBHs ever seen (17 billion suns) that happens to reside in a galaxy that is too small for it. A team from the Max Planck Institute for Astronomy in Heidelberg, Germany used data from the Hobby-Eberly Telescope and archived data from Hubble to determine that the SMBH in NGC 1277 is 17% of the mass of its host galaxy, even though the elliptical galaxy of such size should only have one which is 0.1%. And guess what: four other galaxies have been found to exhibit similar conditions to 1277. Because ellipticals are older galaxies that have merged with other galaxies, perhaps the SMBHs did as well and thus grew as they became and ate gas and dust from around them (Max Planck Institute).
And then there are Ultra Compact Dwarfs (UCD), which are 500 times smaller than our Milky Way. And in M60-UCD-1, found by Anil C. Seth of the University of Utah and detailed in a September 17, 2014 issue of Nature, is the lightest object known to have a SMBH. Scientists also suspect that these could have arisen from galactic collisions, but these are even denser with stars that elliptical galaxies. The determining factor of is a SMBH was present was star motion around the core of the galaxy, which according to data from Hubble and the Gemini North put the stars at a velocity of 100 kilometers per second (as compared to the outer stars which moved at 50 kilometers per second. The mass of the SMBH is clocked in at 15% that of M60 (Freeman, Rzetelny).
No So Fast
NGC 4342 and NGC 4291 seem to be two galaxies with SMBHs too big to have formed there. So they looked toward tidal striping from a past encounter with another galaxy as a possible formation or introduction. When dark matter readings based off Chandra's data showed no such interaction, scientists then began to wonder if an active phase in the past led to blasts of radiation that has obscured some of the mass from our telescopes. This could perhaps be a reason for the seemingly miscorrelation of some SMBH to their galaxy. If some of the mass is hidden, then the host galaxy could be larger than suspected and thus the ratio could be correct (Chandra “Black Hole Growth”).
And then there are ancient blazars, or highly active SMBHs. Many have been seen 1.4 - 2.1 billion years post Big Bang, a time frame that many consider to be too early for them to have formed, especially with the low number of galaxies around them. Data from the Fermi Gamma Ray Observatory found some so large that they were a billion times more massive than our own sun! (Klotz)
No easy answers, folks.
Chandra X-ray Observatory. “Black Hole Growth Found to Be Out of Sync.” Astronomy.com. Kalmbach Publishing Co., 12 Jun. 2013. Web. 15 Jan. 2016.
---. “Revealing a Mini-Supermassive Black Hole.” Astronomy.com. Kalmbach Publishing Co., 25 Oct. 2012. Web. 14 Jan. 2016.
Freeman, David. “Supermassive Black Hole Discovered Inside Tiny Dwarf Galaxy.” Huffingtonpost.com. Huffington Post, 19 Sept. 2014. Web. 28 Jun. 2016.
Klotz, Irene. "Superbright Blazars Reveal Monster Black Holes Roamed the Early Universe." seeker.com. Discovery Communications, 31 Jan. 2017. Web. 06 Feb. 2017.
Max Planck Institute. “Giant Black Hole Could Upset Galaxy Evolution Models.” Astronomy.com. Kalmbach Publishing Co., 30 Nov. 2012. Web. 15 Jan. 2016.
Rzetelny, Xaq. “Small Object, Supermassive Black Hole.” Arstechnica.com. Conte Nast., 23 Sept. 2014. Web. 28 Jun. 2016.
© 2017 Leonard Kelley