The Known Universe

The American Museum of Natural History astronomer Ben R. Oppenheimer (a member of the team that found the companion to the star Alcor) is part of the group that produced The Known Universe - a short film produced from real astronomical data that takes the viewer on an amazing trip.

From Dr. Oppenheimer's web site:

Every mountain, planet, satellite, star, galaxy, quasar and our cosmic horizon are represented accurately in both size and position relative to each other, based on our best scientific knowledge to date. No interpolations have been made, and only objects that have actually been observed are included. As a result, you will see vast regions of the universe where we have not yet been able to map the locations of particular types of objects, for various scientific reasons. These gaps are akin to the regions labeled 'terra incognita' in old globes and maps, before people had fully documented the geography of the world. This visualization starts from the mountains of Tibet and takes you swirling though our database out to the furthest reaches of the universe that are observable. As we travel away from Earth, the distance from home is represented in the length of time that light takes to travel the same distance.

The film is based on the Digital Universe Atlas, an on-going project of the American Museum of Natural History and the Hayden Planetarium, which consists of the world's most complete and scientifically accurate four-dimensional map of the universe. This visualization, while demonstrating some of the wealth of the Digital Universe Atlas, features only a fraction of the database.

Too Far to Be Seen

Sometimes it is pretty exciting when you look for something and don't see it. Last April there was a gamma-ray burst (GRB 090423) detected by NASA's SWIFT satellite. One of the first ground-based telescopes to look for the visible light afterglow was the automated 60-inch telescope at Palomar. The 60-inch was imaging the source within three minutes of the satellite's detection of the GRB. The result? The 60-inch didn't see it.


You might not expect that I would devote any time or space on this blog for talking about something that we didn't see. But that non-detection (unlike LCROSS) was pretty exciting.

As Brad Cenko said in his report:

The lack of an optical afterglow, together with the fact that the X-ray column density is consistent with the Galactic value (Krimm et al., GCN 9198), make GRB 090423 an interesting candidate high-redshift event. We encourage observations at longer wavelengths to search for a NIR counterpart.

Translation: This object should be bright, but it wasn't seen in visible light. That means it could be an extremely distant event. So distant, that the expansion of the universe shifted its light completely out of the optical and into the infrared. That was indeed the case.

Telescopes observing the object in the near infrared and radio wavelengths did indeed see the optical afterglow of the event and it is the most distant object ever observed.

How far is it? Just over 13 billion light-years from Earth. GRB 090423 occurred 630 million years after the Big Bang, when the universe was only four percent of its present age of 13.7 billion years. Explosions like this give us a glimpse into the early universe and confirm the idea that massive stars, like the one that blew up creating the gamma-ray burst, existed even back then.

Pushing the limit

Rudolph Minkowski, after a long and distinguished career in astronomy, had his last night of observing on Palomar's 200-inch Hale Telescope on March 29, 1960. It proved to be a good night as he measured the distance to the central galaxy in a cluster of galaxies known as 3C295.

With a redshift of 0.46, 3C295 held the record as the most distant known galaxy cluster until 1975. How far away is it? About 4.8 billion light years.

Modern electronic detectors are much more sensitive to light than the old photographic plates used by Minkowski and others and as such galaxies of vastly greater distances are now known making Minkowski's find seem almost close.