What is the age of a black hole?

 
What is the age of a black hole?

Carla René, Pursuing Double Doctorates in Astrophysics and Applied Mathematics
 

There isn’t any direct means of determining the age of a black hole. YET.
We have determined ages by analysing bodies nearby, and then through the process of elimination and other critical thinking skills, have then been able to arrive at one’s age.
Sometimes, if we’re lucky, we can see one’s formation from the direct observation of a star’s final collapse. NASA has the LBT (Large Binocular Telescope) involved in a survey searching for failed supernovae, since the prevailing idea is that stars of a certain mass will go supernovae before forming a black hole.

For instance, in Galaxy NGC 6946, a spiral galaxy about 22-million light-years away, nicknamed the “Fireworks Galaxy” for the number of supernovae produced (just one of several areas searched by the LBT survey), Astrophysicists and Astronomers from Ohio State University have noticed a pattern: nearly 30% of > 20 M (read: greater than twenty solar masses) that are expected to turn supernova, will fail, and instead, go straight to a black hole.
The most interesting evidence for this, and the most very recent, is that of star N6946-BH1. Below is an image taken in visible light and near-infrared by the Hubble Space Telescope.
Credits: NASA, ESA, and C. Kochanek (OSU)
The panel on the left was taken in 2007 when it was visible, and again in 2015, when only a small amount of radiation was detected in the near-infrared, which they suspect is debris falling onto its accretion disc. In 2009, the star shot up to an apparent brightness of over 1 million times as luminous as our Sun for several months, then suddenly went dark in 2015. Researchers surmise that this was the instant when it formed a black hole. Their results were then published in the Monthly Notices of the Royal Astronomical Society. From this point forward, it will be easy to monitor the age.
After their discovery, and watching it “wink” out of sight, they then turned the Spitzer Space Telescope on the spot where the star had been and scanned for any further infrared radiation, which would indicate the star was still there but merely ocluded by a dust cloud. They turned up zero.
“Scott Adams, a former Ohio State student who recently earned his doctorate doing this work, was able to make a preliminary estimate.
"N6946-BH1 is the only likely failed supernova that we found in the first seven years of our survey. During this period, six normal supernovae have occurred within the galaxies we've been monitoring, suggesting that 10 to 30 percent of massive stars die as failed supernovae."
The sad reality of this, is that we simply do not know why stars won’t go supernovae, instead, going in favour of black hole; we lack sufficient data to give us the reason this happens.
I know this wasn’t your original question, but it’s interesting to note. And I’ll reiterate that we just don’t have sufficient information about black holes to be able to accurately gauge a single hole’s age, other than to watch it at the time it forms and then begin counting forward.

ANAΔΗΜΟΣΙΕΥΣΗ ΑΠΟ QUORA 16/7/2017