## Saturday, June 18, 2011 ... /////

### Black hole devoured a star

Reuters and many others are informing us about a cute observation with a cute interpretation.

On March 28th, 2011, NASA's Swift aircraft has seen an interesting event similar to the gamma ray bursts.

The source, named Sw 1644+57, was analyzed by your humble correspondent's former fellow Harvard junior fellow, Joshua Bloom, who is a big gamma ray burst specialist and who spent lots of time explaining to us the not yet quite settled science about the cause of the gamma ray bursts, aside from the methods of seeing them.

His or their analysis - that was just published in Science - has led to an unusual conclusion: the gamma ray flash wasn't a real gamma ray burst.

Instead, a supermassive black hole (millions of solar masses, similar to the black hole at the center of the Milky Way) devoured a star (similar to the Sun). It was a really good star. So the Universe had to create a new star and it wasn't that good. It's kind of a bummer. ;-)

More seriously, Bloom says that the event took place 3.8 billion light years away, in the constellation Draco. Thank God because the amount of energy that was released during the short time exceeded the solar output by very many orders of magnitude - well, twelve, I don't want to scare you. But I do want to inform you. 10% of the rest energy E=mc^2 of the Sun was released within 11 days or so; the Sun needs about 100 billion years (ten times its lifetime) to release the same energy.

Bloom et al. (Science, abstract, technical)

Science Magazine (popular summary)

A more fuzzy paper in Science (about the same event)

University of Berkeley (press release)

Bloom explains the finding (audio)

The New York Times, NPR (warning: Ira Flatow invites... Lawrence Krauss... and Joshua Bloom), Ars Technica
Bloom estimates that each galaxy or each black hole only experiences such an event once in 1-100 million years or so. Reuters wrote a first sentence that sounds crazy: we won't see a similar event for millions of years. Well, if that were the case, Joshua Bloom would be really lucky to see it. ;-)

What they meant is that if we look at the very same black hole, it will do the same thing in a million of years again.

Note that the astronomers couldn't ever see the star inside the black hole. The star was gradually and graaddduuuaallly approaching the event horizon and the signal it was sending was getting weaker, slower, and increasingly more redshifted. The weakening signal could be observed for two weeks or so; in fact, it still shows something now, 2.5 months later. At the beginning, there was a period of 100 seconds in which the gamma ray output changed by the factor of two.

A fascinating collision near Pilsen

A devoured star is amazing but something similar has occurred 4.5 miles from my home today, on Saturday, at 11 a.m.

A few more pictures are here...

At a grade crossing in Chrást near Pilsen - which your humble correspondent has crossed about 500 times by bike and 500 times by the train, and dozens of times with a car - a Pilsner public transportation bus on the line #52 suddenly got stuck right on the tracks. You know, that was a pretty inconvenient place to get stuck because a very fast train from Prague to Munich was just approaching the crossing.

If you have ever watched some movies about Dr James Bond, you know what happened next. The driver had 90 seconds before the collision so he just screamed at the passengers - Get out of here. The passengers got out of there and in a few more seconds, the train smashed the bus and despite the already reduced speed, the train dragged the bus for 50 meters or so with it. Up to 2 negligible injuries in the train, no one got even injured! ;-)

River Berounka will remain Berounka

The river near Chrást - the place of the accident - is called Berounka. It's born as the confluence of the four constituent rivers in Pilsen: Mže, Radbuza, Úhlava, Úslava. Berounka is created at the junction of Mže and Radbuza, the two largest component rivers, which is located near the soccer stadium of the extraleague champions.

Since 2006, some Pilsner officials were fighting a crazy battle. They wanted to eliminate the name Berounka because it is a communist artifact. Why? It's because it was recently invented - in the 17th century, more precisely :-) - so it is clearly linked to communism. The proper name of the big river should be Mže (in German: "Mies", in Latin: "Misa", in English: "Thames without Te", because "Temže" is "Thames") which was named in this way at least since the 12th century, hundreds of years before the town of Beroun (20 miles West of Prague) was even founded (which gave the name to Berounka).

I've never understood whether their ambition was to rename the whole river up to Prague where it flows into Moldau (even Otto's "recent" encyclopedia in 1908 used "Mže" up to Prague!), or whether it should have been renamed to Mže only up to a random place in the middle of the river (e.g. up to Beroun). In either case, that would be pretty difficult a change for the watermen! ;-) Finally, the young mayor of Pilsen Mr Baxa has decided that the fight - initiated by a puritan historian - was hopeless (and, well, silly) today so Berounka will stay Berounka and the Pilsner officials will hopefully stop wasting time with idiocies. :-)

Watermen sailing Berounka

In the 17th century, we didn't have communism yet. I am conservative enough but the idea that using "modern" names from the 17th century is already a sign of modernist degradation seems a little bit over the edge to me. Some things may get renamed over time and in the course of the 20th century, Berounka has simply beaten Mže as the preferred name in the whole length between Pilsen and Prague.

Indeed, Berounka is a kind of a modern name because it helps you to figure out that its position may have something to do with Beroun. And Mže hasn't died away, either. It's still the river up to the confluence with Radbuza where they produce Berounka.