Eight Minutes Old

From today, Thursday (June 25) till Saturday (June 27), there is the “SternenZelt” (Star-Tent) on the Muensterplatz in Bonn (open from 10a.m.-8p.m., Saturday until 10p.m.). As a part of the “International Year of Astronomy” (IYA), scientists and research institutes from our region present astronomy, answer questions and show some of their work to the general public. Everybody is invited to come, it is free and I’ll be there this morning, so if I am in the mood I’ll write something about this later. The announcement an information on the “SternenZelt”-website is in German, but as science is mainly done in English I’m sure everybody will be happy to answer your questions in English, too.

UPDATE: I’ve been there for six hours. It was very nice, the tent is not too big but there are plenty of interesting people, presentations and experiments. We had some English-speaking guests, too. I must admit it was almost easier for me to describe radio-astronomy in English than in German.

I was at the booth of the Max-Planck Institute for Radio Astronomy, there were also four from the University (The Observatory on the “Hoher List”, one on galaxies, one from the physics department on cosmic rays and one from the Geodesy showing the potateo-like form of our earth and explaining how this can be measured). Furthermore, the European Southern Observatory (ESO), the German Museum Bonn, the “Deutsches Zentrum für Luft- und Raumfahrt and some amateur astronomers (observing spots on the sun) were present. And lots of interested people, ranging from small children to elderly people. Even though this only was the first day, I think it is not too early to say this event is a success.

Tags: Astronomy, Bonn, Germany, IYA, Radio Astronomy, Radio Telescope, Star Gazer, Star, University of Bonn

Even though I feel like having a writer’s block, I have to write this down, and forcing me to write looks like the easiest way out, too.

We usually have lunch at a nearby canteen of a big telecommunications-company. Today, there was a group of people sitting nearby and behaving so utterly “German”. While eating, they were complaining about the food, the cook and the fact that all their complains are ignored. They were writing letters and hoping the chef to be fired. Because the fried potatoes were in part too dark (others were not dark enough). This went on for a quarter of an hour. They even complained about the chocolate-covered strawberry that was offered for free today. They do not need a free strawberry, but the food should be better.
I mean, what do they expect for 4 Euros? The food isn’t bad, they should have a look at the students’ canteen… They were feeling way to important and I could not stop to grin. On the other hand, maybe they need to have something to complain about. I am opposed of stereotypes, but this urge to complain is really common in Germany, I’m afraid.
Finally they changed their topic and I learned that the Iranian Election, a Persian TV station in the US, the media in general, the opening of China to capitalistic endeavours and Adolf Hitler’s propaganda and election was planned, organized and financed by a secret group of elitist people that ruled our world for hundreds of years. Uff.
I was happy I had finished eating by then. This wasn’t funny anymore, but one more reason to avoid the business world.

Fnord.

Friday, as it was the last day of the conference, included a final discussion. Here, as in the shorter discussions before and during the breaks, it again became clear that there is not yet a consensus. That’s actually a good and natural thing, as right now there is no theory able to explain everything. I’m happy that most people, as convinced as they might be by the theory they prefer, still enjoy a discussion, dialog and are open minded to attend such a controversial meeting.

There was quite some media coverage of the conference, the following is a short selection of links:

The official press release about the conference: Can not be found anymore because the Bonn University changed it’s website.

Three press releases about the problems for dark matter emerging out of the strange distribution of the Milky Way satellite galaxies:

• One from Bonn University (Germany), Prof. Pavel Kroupa and Dr. Manuel Metz, unfortunately it has the same problem as mentioned above.
• Another from the University of Vienna (Austria), Prof. Gerhard Hensler.
• And number three from the Australian National University, Dr. Helmut Jerjen.

The press releases were covered by many different media, for example here, here and here, also by one of Germany’s leading online newspapers, Spiegel Online. … and some more links.

Furthermore, Prof. Kroupa was interviewed by the German web-radio show “Computer Club 2” (cczwei.de), on the topic of modified gravity laws.

A report (English) about the meeting by Pasquale Galliani, who also was a guest at the Institute during the week after the conference.

An interview (German) with Prof. Pavel Kroupa, organizer of the conference.

And there are two (German) posts in the blog of a colleague who also attended the conference: “TDG Bonn 2009” and “And yet another conference goes by…“.

Tags: Bad Honnef, MOND, Newton, TDGBonn, Antennae Galaxies, Astronomy, Bonn, Conference, Dark Matter, Gravity, Law of gravity, Newtonian Dynamics, Rhine, Simulation, Structure Formation, Tidal Dwarf Galaxies, Tidal Streams, University of Bonn

Read the rest of this entry »

Read the rest of this entry »

What are Tidal Dwarf Galaxies?

Tidal dwarf galaxies (TDGs) are, as the name implies, small. Dwarf galaxies as such (tidal or not) are, compared to the ”usual” galaxies, discs and ellipticals consisting of several 100 billion stars, really dwarfs: TDGs have about ten million stars, only one 10,000th of the Milky Way (but there are smaller ones with as few as several thousand stars, too). Dwarf galaxies are categorized  according to their shape (morphology), there are dwarf Ellipticals (dE, these include dwarf Spheroidals, dSph), irregular galaxies (dI, which can have deformed shapes). One example for the latter is the Small Magellanic Cloud (SMC), a dwarf galaxy which orbits the Milky Way and is deformed by the gravitational field of our galaxy and another neighbouring galaxy, the Large Magellanic Cloud. Both dwarf satellite galaxies can be seen in the southern hemisphere with the bare eye. Maybe dwarf versions of spiral galaxies exist, too, but there is debate on this issue. As they are small and have few stars, dwarf galaxies are very dim. They have few gas and most are rather diffuse structures.

Now, these are dwarf galaxies, but what makes a dwarf a tidal one? For this one has to consider how they formed. While most galaxies are assumed to have formed early in the universe (see Section “Classical” galaxy formation below), there are exceptions.
Galaxies are not  fixed in space, they move around and sometimes can approach to relatively short distances. They might even merge to form a bigger one. In these interactions, the galaxies swing around each other, the gravity of the galaxies pull them into new directions. This results in “tidal forces” acting on the material of the galaxies: stars and gas. This is similar to the tides on earth, lifting the water of the oceans by some meters.

While the earth can keep it’s water, galaxies interactions are much more violent. The different forces acting on both sides of the galaxies result in matter thrown out of them into the intergalactic space. This usually happens along so-called “tidal tails”. One beautiful example are the antenna galaxies, a pair of merging galaxies with two very pronounced tidal tails. I think you will notice them at once in the picture on the left, taken with the Hubble Space Telescope (created by Brad Whitmore (STScI) and NASA).

In contrast to the tides on earth, these interactions take millions of years. Thus we can only see one snapshot of these interactions. But we can make models of galaxies in the computer and calculate what happens to them when these, for example, pass another galaxy.

In this movie of one of my simulations, you see the yellow disc galaxy passes by another galaxy. As it is dragged around, material of the disc is torn out in two directions, towards the other galaxy and into the opposite direction (like in earth, where there is always a high tide on two sides. That’s why we have high tides about twice a day). BTW: It’s so cool to make movie!

Now, within these tidal tails, matter can a clump under it’s own gravity. When there is enough matter collected, stars an mostly gas, new stars can form out of the latter. That way, within the tidal tails a new galaxy is born. Of course it is a small galaxy, as only a fraction of the original galaxy’s material finds itself within the tidal tail. Thus, these galaxies are referred to as Tidal Dwarf Galaxies. The first one has been discovered in the tidal tails of  above mentioned Antennea galaxies by Mirabel, Dottori & Lutz in 1992. So you can see this still is a relatively new topic. But it could have strong effects on our understanding of the universe. To explain this, we first need to know how galaxies form usually …

Read the rest of this entry »

To be able to give you some insights into next week’s conference, I’ve ordered a PCMCIA Compact Flash adapter for my notebook, installed GIMP and got a USB stick. So I can in-time transfer pictures from my girlfriend’s digital camera which I can use for some time. So for the next days, I will include digital pictures in the blog. The following post is my test of this setup.

My Moo-Cards, mini business cards of 2.8 x 7 cm size, have arrived. It took them only one week to get here from the UK. And I must admit: they turned out to be totally cool. Of course they show my black and white photos on one side, which don’t show any color cast and are reasonably sharp. The writing on the other side is well done. And the format is unique and absolutely sufficient occupy my name, phone, address and blog-address. It’s interesting to have a look at my pictures in such a special aspect ratio, surprisingly it works well for many photos.

I’ve also ordered some postcards. Their envelope unfortunately was damaged during shipment, so one corner of most cards isn’t as perfect as possible. And I would suggest not to order postcards and mini-cards at one, as the latter are shipped in a nice white box. Which is made of plastic. And has hard edges and corners. So unfortunately there are dents on the first two postcards. But overall they are nice, not as amazing as the mini-cards because they lack some contrast, the dark parts are a bit too light for my taste. But the back showing all 20 motifs on the right of the card is a great feature. But have a look on your own: