This post introduces a new feature on the blog page and then provides a review of a book and a distinguished physics lecture and concludes with some additional follow up discussion on the constraints on the collapse of molecular clouds into protostars or proto-galaxies.
First, the new blog page feature is a location where a calendar of upcoming meetings and conferences can be found. Our plan is to update this page with new conferences and meetings of interest to physicist wannabes or astronomers as the events become known. You can find this calendar of events on this blog main page under the category of meetings, conferences and events calendar. I wanted to use a real-time, user-friendly calendar with clickable objects, etc. that we are used to seeing, but sorry, developing that type of object was way beyond my webpage skills. For your convenience a direct link to that page is shown below:
As you can see the next upcoming event on the calendar is the Dark Matter 2018 conference at UCLA. It will be very interesting to get the latest details on the search for and understanding of dark matter. See you there.
Secondly, one of the side benefits of attending the Kip Thorne interview at the Science Salon last week was the giveaway of free books. Attendees could select and carry off two books of their choosing and luckily, one of my choices turned out to be an absolute gem. "Spooky Action at a Distance", by George Musser, presents a history of . I know in my tortured study of quantum mechanics, where I am just getting proficient enough to write the equations governing some types of predictions, that you can see how to calculate and get the right answer for the laboratory experiment, it still is a bit confusing how and why nature works that way that seems to contradiction in the words we use to describe what happened. Anyway, if you like this type of discussion, check out the book, its great!
|Fantastic book and discussion of locality and non-locality in the history of physics|
I also was able to get on Professor Craig Roberts, Argonne National Laboratory presented the CSULB Distinguished Lecture in Physics on the topic of "Laying the God Particle to Rest." Roberts went through the history of the Higgs particle, called the God Particle, by one author, which is attributed to how the Higgs gives mass to ordinary particles. The Higgs was the last remaining piece of the Standard Model and it has taken about 50 years for this final completion of the theory that summarizes everything known about particle physics. The problem that Craig goes into is that even though the Higgs was invented to give mass to ordinary particles, it only works for the electron and does not provide a way of calculating the mass of the proton and neutron, whose mass is mostly made up of the gluons which hold the quarks bound inside each of those particles. There are still too many unknown couplings that have to be supplied by hand or based on experimental measurement that there is no theoretical basis for determining the coupling constants. So, there is still a lot of fundamental unknowns to be understood and developed. He says that this computational effort being led by Quantum Chromodynamics is making progress but there is still way too much difficulty in actually doing the calculations, even with the largest supercomputers. This is still a major problem in physics, even though the current model makes all the right predications that can currently be made in the largest particle colliders. So, yes, the Higgs was great, but we have more work to do to get to the fundamental physics of mass of protons and neutrons, so let the God particle rest in peace as we continue to try to make more theoretical progress.
I really enjoyed the presentation, but my understanding of the Standard Model and QCD is not sufficient to really get into those kind of details.
|Craig Roberts at CSULB Distinguished Lecture explaining why the Higgs particle should RIP|
Finally, I want to go a bit further into this topic of formation of stars and galaxies due to the collapse of large gas clouds that was briefly discussed in the previous posting. Remember that we described how one theory of supermassive black holes are formed supposes that a nearby, helper galaxy, through its own production of supernovas, which generate shock waves in the first galaxy, which enables the collapse of a major portion of the gas cloud directly to a supermassive black hole. That is pretty neat stuff, but for my discussion, I wanted to show some of the charts from this recent book, "An Introduction to Galaxies and Cosmology", edited by Jones, Lambourne and Serjeant, that I have been reading to get a more basic introduction to how gas clouds collapse. Remember that the key constraints on collapse are how the gas cools off and how angular momentum is shed so that the gas can actually collapse.
But first, let's consider the importance of dark matter that has been found to be so essential in enabling the initial collapse from the initially very smooth gas from the big bang. If dark matter were not present, there apparently has not been enough time for the normal, baryonic matter, to begin to clump together. Dark matter did not face the same constraints, to be reviewed in the next section, and was able to clump together gravitationally very early on after the big bang. This can most easily be seen by looking at various simulation models, such as the Millennium Simulation, shown below.
|Millennium simulation shows impact of dark matter on galaxy formation (Source: Boylan-Kolchin, et al, 0903.3041v2)|
Ok, so dark matter makes the transition from a uniformly distributed collection of hot gas into gravity dominated regions where normal baryonic matter can also begin to collapse. So what other conditions are present that get in the way of the collapse of baryons?
The figure from the "Introduction to Galaxies and Cosmology" textbook identifies one of the first barriers to collapse. Until the time of recombination, usually stated as about 380,000 years after the big bang, the radiation pressure was so high that protons and electrons could not remain bound to each other. Only after the universe had cooled enough that stable hydrogen atoms could exist was it possible for gravity to start to win out over radiation. The figure below shows that dark matter, here identified as WIMPs, started to collapse before recombination, but that the normal matter could only begin to collapse after recombination. You can see that at the time of recombination, the dark matter was already seeing 100 times more variation in density than was normal matter.
|Why dark matter clouds can collapse before baryon clouds (Source: "An Introduction to Galaxies and Cosmology")|
Another key constraint is the temperature of the collapsing cloud. Too high of temperature and the resulting kinetic motion of the atoms can counter the attractive force of gravity. The relationship between the gas temperature and the mass of the gas cloud at which collapse is possible is termed Jeans mass law. If the actual mass of the gas cloud is not greater than the Jeans mass, the cloud cannot collapse until conditions change so that the cloud either gains more mass or losses more energy and cools off.
|Gas clouds can collapse when Jeans mass conditions are met (Source: "An Introduction to Galaxies and Cosmology")|
Finally, even though we have skipped a lot of details, it is interesting to look at the progression from collapse of molecular clouds to the merger and collapse of entire galaxies. As gravity continues to form more stars and galaxies, it also drives the evolution and merger of galaxies themselves. The "merger tree" below shows the possible history of one large elliptical galaxy. Each of these stages along this merger journey are more complicated than briefly noted here.
Until next time,
Resident Astronomer George