A black hole two billion times more massive than the Sun is not something you find every day. Even more unusual is to find it embedded in a quasar that is 12.7 billion light years from Earth. But that’s just what Tomotsugu Goto (Japan Aerospace Exploration Agency) seems to have found using the Subaru optical-infrared telescope on Mauna Kea. How a black hole of this mass could have formed only a billion years after the birth of the universe is only one of the questions this find poses.
For the object, found in the direction of Cancer, also shows via its spectrum that much of the hydrogen between the quasar and Earth is ionized. What would cause neutral hydrogen to be converted to ionized hydrogen in this early epoch? Ultraviolet radiation is thought to be the key, but observational evidence helping us understand how and when this occurred has always been tricky to gather for a reionization event that occurred over 12 billion years ago.
Quasars are useful beacons by which to study this reionization. Gamma ray bursts are also helpful in determining how the phenomenon occurred, but they’re brief and sporadic, whereas quasars appear bright and stable over long periods of time. Hence Goto’s plan to investigate still more distant quasars using the same methods he used here: searching the Sloan Digital Sky Survey for objects having the same color in visible light as quasars at 12.7 billion light years distance, then observing the candidate objects on Mauna Kea to eliminate all but the quasars being investigated.
Image: The CCD image of the spectrum. The fact that light is detected between 800 and 830 nanometers indicates that much of the hydrogen between Earth and the quasar must be ionized. Credit: Subaru Telescope, National Astronomical Observatory of Japan (NAOJ).
Centauri Dreams‘ note: When the early universe cooled sufficiently, electrons and protons combined to produce neutral hydrogen, an event that probably began about 300,000 years after the Big Bang. Today most of that hydrogen has been ionized, splitting into separate electrons and protons; the absorption of light at particular wavelengths causes this to happen. Because the spectrum of this quasar shows there was not enough neutral hydrogen to absorb the light between the wavelengths of 800 to 830 nanometers, we can put further constraints on the state of ionization in the early universe.
A good backgrounder on all this, with links to other important quasar work, is available from Rennan Barkana (Tel Aviv University). Barkana is also the author of “The First Stars in the Universe and Cosmic Reionization,” Science 313. No. 5789 (18 August 2006), pp. 931-934, with abstract available here.