Well the weather is getting a little better for some astronomical observations, but this week we follow up on early galaxy formation as pickles rather than spheroids and then look back into the past discoveries of x-ray objects, look at Maxwell's faithful friend and the 100 year centennial of the measurement of bending of light observed during the total solar eclipse of May 29, 1919.
Now, when Visionary Physicist Dr. Don, alerted us to the upcoming UCI seminar presentation by Dr. Joel Primack, UCSC, we knew we had to get this seminar on our schedule. Readers of this blog will of course know that three previous blogs posts of November 1, 2017, November 26, 2017 and June 8, 2018 all had some reference to Dr. Primack's work or books as he has been such a leading scientist and cosmologist. Thanks for the alert, Don!
In this UCI seminar presentation entitled "Comparing Galaxy Formation Simulations and Observations with Machine Learning", Dr. Primack described how the early formation of galaxies really began as more "pickle" shaped than spheroidal. In the introductory slide below you can see how as galaxies start to form the amount of gas decreases, because it is being tied up in stars, and the amount of initial dark matter just increases slightly as more and more material is falling in towards the gravitational potential well. Dr. Primack mentioned that when he was studying galaxy formation it was almost common knowledge that they must have started as spheroidal collections of gas, even though many early observations had clearly shown the more prolate or pickle shape.
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| Joel Primack, UCSC, discusses prolate structure of early galaxies at UCI Seminar (Source: Palmia Observatory) |
So, now why is the pickle shape the new standard form used to describe galaxy formation? In the figure below, taken from the published paper, you can see the various shapes under consideration. If the dimensions of the two axes are about the same value, then the shape is considered spheroidal, but if one axis is much longer than the other, then the shape is more pickle like or prolate as it says here. So, if we were to measure the dimensions of galaxies along these two dimensions, a and b, and compare these measurements along with the redshift of the galaxies, which corresponds to the age of the galaxies, we can see what the shape of the early galaxies was.
The presentation included many interesting slides but rather than show again some photographs taken during the seminar, let's look at the original material taken from the original paper, "The Evolution of Galaxy Shapes in CANDELS: from prolate to oblate."
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| The Evolution of Galaxy Shapes: From Prolate to Oblate (Primack+, 1805.12331v1, 31 May 2018) |
The study makes use of galaxy images collected using the HST in the large datasets produced in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). An example of a galaxy image, taken from Figure 15 of the paper, is shown below.
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So, after reviewing many images of galaxies at various redshifts the results can be plotted as shown below. You can see here that the older the galaxy is, that is the more redshifted in shows up in the image, the more prolate the structure. So, even though many of us grew up with the image of galaxies forming as a spherical ball of collapsing gas, the real picture and history is more complicated and the original shape is now thought to be more prolate or pickle shaped.
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Primack discussed the formation of early galaxies along the filaments of dark matter in the early universe. Afterwards, I found this simulation image of dark matter filaments. Yes, the filaments are long narrow structures, so why wouldn't early galaxies sort of form like pickles on a wire? Thanks to Dr. Primack for very interesting presentation!
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| Simulation of expected cosmic web filaments of dark matter forming after the big bang (Source: Wikipedia) |
After the UCI seminar there was few spare minutes to catch up on studying the emission of radiation from neutron stars. In the previous blog of May 26, we saw that material falling into black holes result in emission over a wide frequency spectrum. In searching for the spectrum from neutron star pulsars, I saw a reference to the first detection of x-rays from an extra-solar source outside the solar system. Hmm, let's follow up on this discovery from 1962 and look a bit more into the history and details of the discovery.
The image below is from a 1962 paper published in Physical Review Letters by Riccardo Giacconi, et al, titled "Evidence for x-rays from sources outside the solar system." The image shows the raw data taken from x-rays sensors aboard an Aerobee rocket that was launched so that the sensors were above the Earth's atmosphere, which would have blocked and absorbed the x-ray radiation. You can see a peak in the collected data, but what source outside the solar system does this come from?
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| Evidence for x-rays from sources outside the solar system (Giacconi+, Physical Review Letters, Dec 1, 1962) |
Well given the orientation of the rocket and sensors and an indication of the azimuth and the time of observations, we can calculate where on the sky the sensors were pointing. So, in the plot below you can see that Giacconi identified the x-ray source as located in the constellation Scorpio. Pretty neat! It turns out that that x-ray source, now called Sco X-1, is one of the brightest x-ray sources in the sky and now there are hundreds if not thousands of known x-ray sources. Sco X-1 is now recognized as a binary star system composed of a neutron star and low mass companion star.
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Now, I worked on guided missile autopilots in the 70's, so I imagined the early experimenters would have used accelerometers and such instruments to monitor the position of the rocket during flight so that the orientation of the x-ray detectors could be traced back to identify where in the sky the sensors were pointed. It turns out in 1962 the x-ray data was taken during just the straight vertical rise of the rocket. The rocket was uncontrolled and did not rely on feedback control systems with gyros and accelerometers, but relied only on aerodynamic fins to help stabilize the flight which rotated at 2 revolutions per second. The three x-ray sensors were mounted symmetrically around the rocket, oriented to point upwards at about 55 degrees. Then some (unspecified) optical alignment device identified the azimuth orientation of the rocket and so from that and the rotation rate and assumed vertical position, the sky location can be calculated. The paper goes into more of the details and even says that one of the three x-ray sensors malfunctioned and was not used in the analysis. Also just in case you were wondering, the x-ray sensors were covered with material so that the sensors would not be affected by visible or UV sunlight.
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| Aerobee Rocket (Source: White Sands Missile Range Museum) |
So, with the clouds out and about, it was more time to watch some livestreamed presentations at the Institute of Advanced Studies (IAS) in Princeton. Math Whiz Dave had alerted us to watch for this livestreamed event and I'm glad I tuned in on it. The topic of the presentations was "The Universe Speaks in Numbers" and I sat down to watch some of the presentations with Astronomer Assistants Ruby and Danny. Thanks for the alert, Dave, all of us enjoyed the presentations!
Graham Farmelo talked about how James Clerk Maxwell described how the universe speaks in numbers though the now famous Maxwell Equations of Electromagnetism. One of his slides shows a portrait of Maxwell, with wife Katherine, who also was a physicist in her own right, and the faithful dog. At this point, Astronomer Assistants Ruby and Danny wanted to know more about the dog. What is the dog's name?
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| James C. Maxwell, Wife Katherine, and faithful friend (Source: G. Farmelo, IAS Presentation, May 29, 2019) |
Well the name of the dog was not included in that presentation, but some independent searching on the internet came up with some more information. Check out this image of the Maxwell statue in Edinburgh, Canada. Now Resident Astronomer Peggy and I visited Edinburgh maybe 20 years ago now and I sort of remember seeing some statue like this but could not find any photographs of it. But the point is to notice that included in this statue is not the wife, but the faithful dog, not that the wife was not faithful. Anyway James Rautio published a little article in the IEEE Microwave Magazine with more details about the statue and the dog's name.
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| Statue of Maxwell in Edinburgh (Source: J. Rautio, IEEE Microwave Magazine) |
Here you can see a larger view of the dog faithfully laying at Maxwell's side. Well it turns out the dog's name is Toby. So there you go, Ruby and Danny, the dog's name is Toby!
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| Statue of Maxwell in Edinburgh includes his faithful dog, Toby (Source: J. Rautio, IEEE Microwave Magazine) |
Separately, another way the universe speaks in numbers is through astronomical predictions. It turns out that May 29 is the centenary of the famous total solar eclipse expedition that was to verify the bending of light by the gravity, as observed for starlight passing close to the edge of the sun. Hmm, I wonder if our modern sky location tools will be able to show the location of the sun and moon back on May 29, 1919? Yep, it seems to work ok. Take a look at this Sky Safari Pro screenshot with the date set to May 29, 1919 and the location set to Principe Island, off the coast of West Africa. We modern day observers have it so easy compared to the early explorers from whom we have learned so much. What a 100 years of progress have achieve!
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| Sky Safari Pro screenshot for total solar eclipse at Principe on May 29, 1919 (Source: Palmia Observatory) |
Until next time,
Resident Astronomer George
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