Archive for the 'galaxies' Category

All Creatures Great and Small

The previous post was a farewell to black holes in the class, not here on the blog. (And it was not quite a farewell there either, since the midterm yesterday was all about the properties of the Reissner-Nordström black hole, representing a black hole with an electric charge, and a nice computation involving cosmic censorship.)

There have been two rather notable discoveries in the black hole astrophysics world this week. The first is the discovery of what seems to be another case of an intermediate mass black hole (there was only one example known before). Not the supermassive ones that live at the centers of galaxies (tens to hundreds of millions of times the mass of our sun), and not stellar mass ones of a few times the mass of our Continue reading ‘All Creatures Great and Small’

Two Rings

Now have a look at this object (and its enlargement on the right):

double einstein rings

What is it? It’s a double Einstein ring! An Einstein ring is formed by gravitational lensing - the bending of light from one object by the gravity of another object - and is typically formed when a distant galaxy lines up with another, closer galaxy. The result is a rather nice ring shape.

To find a double Einstein ring is rare! In fact, this is the first one that’s been announced. Not only is it novel, it can also use used to do a good deal of science, such Continue reading ‘Two Rings’

The Flat Universe

chuck steidelkc coleWhile searching through their site to find something else, I noticed that there was a conversation on KPCC’s Zocalo between science writer K C Cole and Astrophysicist Chuck Steidel not long ago. Have a look at their listing of past conversations here - there’s a lot of good stuff about various topics and people in the Los Angeles area. I listened to it, and it’s very interesting indeed.

It is not quite your usual light touch conversation that you hear on public radio - it is a little more involved, taking you a bit further (without losing you) and gives you more insights into the work, the puzzles, the discoveries and the hopes for future ones. As a journalist, and the guest host of the program, K C Cole knows her material, and so is able to steer things rather well, while inserting useful remarks to help the listener keep up. This might be perfect listening if you want to get a sense of what it’s like to work in Chuck’s area of expertise (finding and characterizing the youngest galaxies and understanding their cosmological implications), either out of general curiosity or if you’re planning a career in that area. Take out some time and have a listen. Here’s the blurb from the site:

Continue reading ‘The Flat Universe’

Dark Puzzles

composite cluster image - dark matter

(Click for larger view.)

This lovely composite image of Abell 520 that includes an inferred distribution of dark Continue reading ‘Dark Puzzles’

The Scary Universe?

Ok, there’s “The Elegant Universe”, and “The Ambidextrous Universe”…. even “Stephen Hawking’s Universe”… and so on for these titles. But how about “The Scary Universe” or “The Dangerous Universe”? (Personally, I wish we’d just stop with the whole “The fill-in-the-blank Universe” stuff, so I probably should have not written this first paragraph.)

Well, I myself don’t think of the Universe that way, but tonight (at 9:00pm) the History Channel will be presenting the next show in their series (called “The Universe”), which is about (they say) the Most Dangerous Place In The Universe”. It looks as though it will be a survey of various places where a lot of very energetic activity is taking place, powering some of the most powerful phenomena we’ve ever seen, such as quasars, magnetars, and so forth. So black holes will feature quite a bit, I imagine, and although I probably should not really be telling you about it before I’ve had a chance to see it (recall my remarks about the windy shooting conditions), I think (I’m not sure) that I’ll be making an appearance as one of the contributors. (I did not get caught off guard this time.)

The whole “dangerous” motif is a sort of deliberately sensational way of presenting Continue reading ‘The Scary Universe?’

The Walk Up Mount Wilson

[A friend of mine in LA told me today that she was planning to go with a group of friends to do some observing up at the big telescope on Mount Wilson. This put me in mind of a post that I did on CV two years ago (how time flies!) about some of the science done up there at the Mount Wilson Observatory, thoughts surrounding, all combined with a hike up to it that I felt compelled to do upon seeing it from the air. I thought I’d bring that old post back for you to read, with enlargeable pictures as a bonus. Enjoy. -cvj]
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sign to mount wilsonAs you know from an earlier post, I left Aspen on Friday and headed home. This involves changing planes at Denver, and then flying over the strange, beautiful, and changing landscape West to Los Angeles. It only takes about a couple of hours. I was thinking hard about our discussion about the Greatest Physics Paper! and trying to think of those forgotten examples of great work. The people who’s songs are seldom sung. The unglamourous “bread and butter” works that seldom get written up in the newspapers near the time that they are produced, if ever. These solid works are examples of what every scientist should do as a matter of course: You look at the evidence you have before you, gather more if necessary, make some assumptions, form a hypothesis, and test it against the data. Next, come to a conclusion, and report your results as clearly and honestly as you can, and so on.

Whether or not you have some vision about what it all means does not necessarily qualify or disqualify the resulting paper as a candidate for being a great paper. It can still take its place in the tapestry that is the sum of efforts of generation after generation of physicist to make sense of our world, and find its meaning there.

Mount Wilson Hike -  foliageSo I was thinking about this all, and my mind switched to some recent reading I’d been doing. Simon Singh’s excellent book, “Big Bang” had been on my bedside table recently, and although I’d not had a lot of time to read it, I was curious to dip into it from time to time. This is partly because, while I know several of the stories and the history that he tells, it is always of great value to see how another tells those stories. I always learn something, either in the facts or in the telling.

As we’d been discussing before, Einstein’s papers are modern examples of work that changed our entire view of how the universe that we inhabit is really put together. How can those fail to be top candidates for the best physics papers ever? Same thing for Newton, and for Galileo, etc.

However, it’s easy to forget that for several years after Einstein’s breakthrough with General Relativity [see a later post I did here], the world still thought that the entire universe was just the Milky Way Galaxy. It was not until the year 1923 that Edwin Hubble (in one of his many great contributions) established extremely cleanly that the Andromeda Galaxy was several times further away from the center of the Milky Way than the edge of the Milky Way itself. This was a truly shattering change of perspective Continue reading ‘The Walk Up Mount Wilson’

Andromeda Now Makes Sense

andromeda IRThe Andromeda Galaxy is bigger than previously thought. Perhaps as much as five times bigger. I know that you’re thinking - “Oh, that’s because most of it is dark matter, right?” No, this is not another dark matter story. In fact, there are many newly discovered stars from a recent study! The suburbs of the galaxy are much more extensive than previously identified. It’s rather good news, since the galaxy makes more sense than it did before, in the context of our understanding of how galaxies form and evolve. (Image above is of Andromeda in the infra-red, from NASA.)

The point here is that current theories of evolution for galaxies have the oldest stars Continue reading ‘Andromeda Now Makes Sense’

Dark Matter in 3D

Have a look at this:

hubble 3d dark matter

What is it? It is an image of part of the three dimensional (see below) distribution of clumps of dark matter in our universe, produced by an extensive survey using the Hubble telescope. How did they produce it, given that dark matter is -by definition- not visible? They deduced the presence of the chunks of dark matter by looking at the Continue reading ‘Dark Matter in 3D’

Some Observations at Griffith Observatory

So I must apologize. I went to the preview of the Griffith Observatory so long ago now and did promise to blog about it with more than just one nice picture, but it did not happen. Partly because I had to go back across the Atlantic to do some work, and then got ill over the weekend I was planning to do it, and then..

Griffith Observatory

Anyway, here are some of my thoughts. First note that my two week delay means that this is no longer a scoop, since even the LA Times had a spread on the whole thing on Thursday. A rather nice one as well. I urge you to consult it for a lovely pull-out graphic of the whole site. There is also a special website with picture tours, nifty 360 degree interactive shots of the spaces, and other information. The Griffith opened yesterday.

What they’ve done over the last four or five years is simply shut down the entire building and rethink and redo a great deal of it. How to preserve the lovely 70 year old landmark, while making it even better? Simple question - simple answer: Get $93 million for your project (I find this number, the earth-sun distance in miles, suspicious), and then go underneath the existing building and hollow out about the same amount of space that is has, but underground. Fill it with lots of goodies. And I mean lots and lots. What goodies? We’ll see.

Continue reading ‘Some Observations at Griffith Observatory’

The Lives Of The Stars

Well, I’m back from the visit to the preview of the Griffith Observatory that I mentioned to you I was going to. It was a rather good visit. They organised it well, and -boy!- have they done a great job on the restorations! I’ll try and assemble the several pictures that I took into some sort of narrative for you, and report soon. While you wait, here’s one of my favourites:

main sequence exhibit

This is particularly poignant, in my opinion. The children are looking at the lovely Continue reading ‘The Lives Of The Stars’

Explaining Cosmic Rays

gary zankWell, before disappearing into a long session of thinking about some funny behaviour my strings are up to (more later) I’d like to do a quick report on the departmental colloquium that I went to just now. We had Gary Zank, the Director of the Institute for Geophysics and Planetary Physics of the UC system (he’s based out of UCR) give us a talk entitled: “Particle Acceleration in Cosmic Plasmas”, and it was quite fascinating (and very well presented).

It is all about the physics of cosmic rays (here’s a NASA link called Cosmicopia for a little background on them). Here is a section of the abstract he sent to us prior to the talk:

An outstanding problem in astrophysics is to explain the origin of the almost featureless cosmic ray spectrum extending up to energies of some 1020 eV. A very small feature is apparent at between about 1013 – 1015 eV, the “knee.” In the late 1970’s, a suite of papers was published establishing the idea of diffusive shock acceleration for cosmic rays, essentially a first-order Fermi mechanism, which appeared to provide an explanation for the observed cosmic ray spectrum up to the knee. Diffusive shock acceleration is probably the most widely used particle acceleration mechanism in astrophysics and space physics, yet the theory is based on some stringent simplifications. The detailed [plasma] physics of the acceleration mechanism requires elucidation. We are fortunate in that very detailed observations of particle acceleration at shock waves, particularly in the guise of Space Weather, are providing considerable experimental insight into the basic physics of particle acceleration at a shock wave.

He gave us an overview of the remarkably detailed series of studies that his group has been carrying out (with the aid of an impressive multitude of computer simulations of the magnetohydrodynamics involved) in converting the various suggested acceleration mechanisms into detailed output that can be compared to experimental observations. Here’s a bit from their website:

The dynamical acceleration of particles at shocks waves propagating in the heliosphere is very poorly understood, yet shock waves are ubiquitous and almost all shocks are observed to energize ions and electrons. An understanding of particle acceleration at solar wind shocks has far reaching astrophysical implications. Furthermore, since energetic particles accelerated in either solar flares or in CME-driven shocks arrive at the Earth well before solar ejecta driven disturbances, an understanding of particle acceleration at interplanetary shocks is an integral part of the NSF and NASA Space Weather program.

He spoke quite a bit about shock wave mechanisms and how they work in supernovae Continue reading ‘Explaining Cosmic Rays’

From Dwarf Planets to Hobbit Galaxies

dwarf galaxyI learned from an article in New Scientist by David Shiga that there have been recently found four more small satellite galaxies of our Milky Way galaxy.

The satellites are dwarf galaxies a few hundred to a few thousand light years across. The tiny galaxies are thought to be the building blocks of large galaxies, such as our own Milky Way – which is about 100,000 light years wide.

As you may know, we’ve known for some time that there have been such satellites (the number knwon has gone from 10 to 20 in the last two years, and some models expect as many as 50), but the small ones are very hard to detect. How do you distinguish them from other stars in the way? As part of the Sloan Digital Sky Survey (SDSS), the researchers have been looking for….

the particular types of stars expected to lie in dwarf galaxies, then detect the dwarfs as slight “overdensities” in these types of stars – patches of the sky where there are more of the stars than in surrounding areas.

The Cambridge team named them after the constellations in which they were found:

[…] Coma Berenices, Canes Venatici II, Hercules, and Leo IV, all of them lie between roughly 100,000 and 500,000 light years from Earth.

[…]The largest and smallest are Hercules and Coma Berenices, which are about 1000 and 200 light years across, respectively. Like most of the other dwarfs discovered by SDSS, the new finds are much smaller and fainter than the 10 dwarfs that were known previously, [Vasily] Belokurov [the team leader] says. “They should not really be called dwarfs – they are more like hobbits,” he told New Scientist.

Hobbits. Right. Does that make the Milky Way a Cave Troll? Or maybe a Numenorian? (Picture above is one of them. This one’s Farmer Maggot, I think. They’re not as Continue reading ‘From Dwarf Planets to Hobbit Galaxies’