Astronomy Questions: APOD = Astronomy Picture Of the Day 1. The APOD http://apod

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Astronomy Questions:

APOD = Astronomy Picture Of the Day

1. The APOD http://apod.nasa.gov/apod/ap140928.html for 2014 September 28 shows a composite radio and X-ray image of a pair of galaxies called 3C 75 in the Perseus cluster. The explanation states that the two galaxies are in the process of merging and that such mergers are "expected to be intense sources of gravitational waves". I understand that merging supermassive black holes should give off gravitational waves that could be detected by measurements of shifts of the arrival times of the pulses from radio pulsars as gravitational waves perturb spacetime (for example, the NANOGrav project). If we continue to build and use powerful radio telescopes to measure more pulsars more precisely, do you think that we will be able to detect gravitational waves from the 3C 75 merging pair (i.e., this particular pair of galaxies) in the next 100 years? Of course, I want to know what motivates your answer.

2. The APOD http://apod.nasa.gov/apod/ap110907.html for 2011 September 7 shows an image (well, just a point of light) of a star that apparently has fewer metals than predicted for any stars. I understand that hydrogen and helium and a trace amount of lithium was produced in the "epoch of primordial nucleosynthesis" about 3 minutes after the Big Bang. Why did primordial nucleosynthesis happen only at that time (3 minutes after the BB), not earlier and not later, and why was the primordial abundance set at about 75% of the mass in hydrogen, 25% in helium, a tiny amount of lithium, beryllium and boron and no elements heavier than that?

3. The APOD http://apod.nasa.gov/apod/ap071016.html for 2007 October 16 shows two images taken about 3.5 months apart of a supernova which has been shown to be of supernova classification "Type II". The observations that have led to the discovery that the expansion of the universe is accelerating were of Supernova "Type Ia". The explanation says that Type II supernovae are not useful as probes of dark energy because "astronomers don't understand how to accurately recover their intrinsic brightness". What exactly is the problem with using SNe Type II in the study of dark energy? In particular, hoiw can we use observations of supernovae to show that the expansion of the universe is accelerating and why the observations work for Ia's and not II's?

4. The APOD http://apod.nasa.gov/apod/ap031231.html for 2003 December 31 shows the images of the cosmic microwave background radiation made by the Wilkinson Microwave Anisotropy probe (WMAP) where the whole sky is shown divided into two hemispheres. I understand that a principal goal of the various satellites that have studied the CMB is to establish the typical size of the blotches in the map. Why do we want to know what the typical size is and what does the size of the average blotch tell us about the history of the universe?

5. The APOD http://apod.nasa.gov/apod/ap000123.html for 2000 Jan 23 shows a cartoon depiction of the coded radio message transmitted from Arecibo in 1974 towards the globular cluster M13. I seem to remember reading about the sending of this message from the Arecibo Observatory when I was at Cornell myself. I also seem to remember some discussion about the fact that if the universe were much younger (say, less than 1 billion years old), we (human beings here on Planet Earth) could not exist. Can you explain (briefly) the scientific logic behind that argument for me?

Explanation / Answer

Ans) The two bright source at the centre of this composite x-ray , radio image are co-orbitting supermassive black holes powering the gaint radio source 3C75. Surrounded by multimillion degree x-ray emitting gas, and blasting out jet of relative particles the supermassive black holes are seperated by 25,000 light years. At the cores of two merging galaxies in the Abell 400 galaxy cluster they are some 300 milion light year away. Astronomers conclude that these two supermassive black holes are bound together by gravity in a binary system.

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