* TheSpacewriter

Separating Darks from Lights

Galaxy Cluster Clash Points out Dark Matter

This image just released today may look like a galaxy cluster with some Photoshop airbrushing on it, but it’s really proof of an effect that had been observed once before but not completely proved. The Hubble Space Telescope and Chandra X-ray Observatory both studied the same area of the sky, looking at a collision of galaxy clusters into a giant supercluster, called MACS J0025.4-1222.  The combined observations provide another clue to the existence and distribution of dark matter. This time the mechanism was provided by the cluster collision. When such objects collide, they pack a heck of a punch, and the energy of that punch separates dark matter from ordinary matter.

Here’s how the Chandra folks describe the mechanics of the collision: two galaxy clusters, each a quadrillion times the mass of the Sun, collided to form the system known as MACS J0025.4-1222. When they merged at speeds of millions of miles per hour, the hot gas in each cluster collided and slowed down, but the dark matter did not.

Optical images from Hubble were used to infer the distribution of the total mass — dark and ordinary matter — using a technique known as gravitational lensing (the blue area shows where light is “bent” as it passes by clumps and regions of dark matter and is influenced by the dark matter’s gravitational pull). Chandra data enabled astronomers to accurately map the position of the ordinary matter, mostly in the form of hot gas, which glows brightly in X-rays (the pink regions.) The separation between the material shown in pink and blue provides direct evidence for dark matter. The fact that it could be separated from baryonic matter in such a powerful collision is another clue to the nature of dark matter.

Understanding this unseen material, particularly how much of it there is in the universe, is key to our understanding of so many other things about the universe. The expansion of the universe, the ordering of large-scale structure (into clusters of galaxies, superclusters of galaxies), and even such aspects of galaxies as their rotation and merger rates are all affected by this dark matter. It permeates the universe, yet it is extraordinarily difficult to detect using conventional observational techniques. It’s “easier” to infer its existence by observing its affect on light, for example. Which is what gravitational lensing does, and what makes it such a useful tool for astronomy.  While we still don’t know the entire story of dark matter, discoveries like these are helping “fill in the puzzle pieces.”

GLAST=Fermi

What it Means

NASA, the Stanford Linear Accelerator Group, and Sonoma State University jointly announced yesterday that their mission, the Gamma-ray Large Area Space Telescope (formerly known as GLAST) is now going by the name Fermi, and it has a nifty new logo to celebrate. I think the incorporation of a stylized active galactic nucleus and a spiraling jet is quite clever.

The spacecraft’s new name honors THE pioneer in high-energy physics, quantum theory, and particle physics, Italian scientist Enrico Fermi, who lived from 1901 to 1954.  He was the first person to figure out how cosmic particles could be accelerated to the high speeds that take them across the universe, and if he had lived to see the telescope that bears his name, he would have been delighted to study the pulsars in our galaxy and the gamma-ray signals from supermassive black holes at the cores of galaxies. His work set the stage for understanding the phenomena we see at these cosmic objects.

Fermi the spacecraft was launched two months ago and has been in testing and calibration mode since then. To celebrate the renaming, Fermi scientists used the Large Area Telescope onboard the spacecraft to “take” an all-sky image showing the glowing gas of the Milky Way, blinking pulsars, and a flaring galaxy billions of light-years away. It’s the result of 95 hours of the instrument’s “first light” observations. By comparison, when NASA’s now-defunct Compton Gamma-ray Observatory, did the same image, it took years of observations to create.

This Fermi image shows gas and dust in the plane of the Milky Way glowing in gamma rays due to collisions with accelerated nuclei called cosmic rays. The famous Crab Nebula and Vela pulsars also shine brightly at these wavelengths. These are fast-spinning neutron stars, which form when massive stars die.  The Crab and Vela pulsars were originally discovered by their radio emissions. The third pulsar shown here, named Geminga and located in Gemini, is not a radio source. It was discovered by an earlier gamma-ray satellite. Fermi is expected to discover many more radio-quiet pulsars, providing key information about how these exotic objects work.

A fourth bright spot in the LAT image lies some 7.1 billion light-years away, far beyond our galaxy. This is 3C 454.3 in Pegasus, a type of active galaxy called a blazar. It’s now undergoing a flaring episode that makes it especially bright. Another instrument onboard the spacecraft, the GBM, has already been recording gamma-ray bursts that occur when massive stars die or neutron stars merge.

At the rate Fermi is studying the sky, I don’t think it will be too long before we start seeing a new set of cosmic images that will bring us new views of the universe in much the same way that the Compton Gamma-ray Observatory did in its heydey.

Telescope Jonesing

To GOTO or not to GOTO?

I was browsing around the other day on the Web, looking at reviews of automated telescopes. Now, mind you, I already have a telescope — a very nice 6″ Sovietski that came with a pier mount you could dock boats to.  It’s a great scope, but it’s not set up in my yard, and so I have to drag it out whenever I want to do any viewing.  Which means, between bad weather at night, clouds of mosquitos, and the weight of the pier mount, it doesn’ get out as often as I’d like it to. Yet, I like to look through scopes at the sky.  I have a smaller AstroScan, which is more portable, but has its limitations.

So, I’ve been considering two options:  1) selling the Sovietski to someone who might use it more than I do and then buying an easier-to-transport automated scope, or b) keeping the Sovietski and buying the automated ’scope anyway.

The cost of the new automated scopes is more than I expected, at least in the 6-inch and higher range.  But they are sweet-looking, and it would be nice to slew from object to object on the few occasions when I have sky, time, and good weather here.  Now, I know there are these debates that still rage in the amateur community about whether ’tis nobler to suffer the slings and arrows of outrageous polar alignment issues that are inherent in both types of scopes.

And, there are those who say you’re not truly doing astronomy if all you do is “point and shoot.” They wax lyrical about the “fun of the chase” in searching out dim, distant fuzzies in the sky. Having done it, I can see their point, somewhat. I don’t subscribe to any such stringent “one-true-way” outlooks; I just wanna get out there and do some guerilla viewing when I can.  There’s no deadline on this; I just have to save the money up to do it, if I decide to get one of these scopes.  But, as for the to GOTO or not to GOTO?  No problems there.