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Chat interaction transcripts - X-Ray Astronomy

megharajoria: Prof can you please explain what are celestial photons basically. I tried to google it but could not find anything relevant to understand this.

Prof. P. C. Agrawal: Celestial photons are the ones that come from any celestial source, galaxy, star, or any other celestial body.

orgspace: Hello Professor Aggarwal, a lot of educators are sitting here at SPACE 1:26 orgspace: Sneh, Priyanka, Rishabh, Sikha, Mila, Jagriti, Padma and myself, Vikrant. some basic questions: Why do we need X-Ray astrnomy?

Prof. Agrawal: x-ray astronomy enables us to study matter under extreme comditions which cannot be studied by means of studies in visible or radio bands.

orgspace: could you please explain extreme conditions

Prof. Agrawal: extreeme condition = matter very high temp, million to billion deg range, matter at density 10^6 to 10^14 gm/cc and particles radiating in magnetic fields in 10^12 to 10^15 gauss region

orgspace: by 10^6 to 10^14 gm/cc do you mean comparable density of a neutron star?

Prof. Agrawal: YES. I mean density which are found in objects such as white dwarf or neutron star. When I say matter at high density I really mean sources of x rays such as white dwarfs and neutron stars which have this kind of density.

orgspace: Could you tell us about some interesting discoveries made wth X-Ray astronomy

salonibhatiaini17: in a binary pulsar, what is the gravitation radiation that is emitted?

Prof. Agrawal: Black holes were only in the realm of imagination till 1971 when the nature of x ray source cygnus X1 was inferred to be a black hole, of more than 7 times the mass of the sun from its rapid x ray intensity variations. Similarly it was inferred from detection of red shifted tail of x ray line in a Serfert galaxy, that it has a black hole of mass 10^9 solar mass at its center thus the generation of energy in the nucleii of active galaxy could be understood by accretion of matter on to this massive black hole. There are several other instances actually in terms of new interesting discoveries from x ray observations.

salonibhatiaini17: in quasars the redshifting is believed to be cosmological

Prof. Agrawal: Correct inference.

salonibhatiaini17: why is the accretion disc model consideed to be the best for powering qquasars?

Prof. Agrawal: There are no alternative models which can explain the high luminosity of quasars, which lie in 10^43 to 10^46 ergs per second range, at present energy release by accretion of matter onto the massive black hole in quasar nuclei is the only viable mechanism for explaining their energy output.

orgspace: How do we measure the collecting area or aperture of X-Ray telescopes?

Prof. Agrawal: The x ray telescopes is calibrated by measuring its intensity of a standard source like Crab Nebula and compaing it with intensity measure with a non imaging insterument such as proportional counter telescope whose area is known by other means

orgspace: hmm interesting

megharajoria: yes

orgspace: on a lighter side, it will be fun to make an X-Ray amateur telescope ;) AT, would you take up the project?

Prof. Agrawal: making of an x ray scvope is avery complex technical challengin thing that needs a lot of high tect facilities, that are not easiliy available in fact in the world, such facilities exist in half a dozen places

salonibhatiaini17: why are the magnetars emitting in xrays as compared to pulsars which emitt mostly in radio

Prof. Agrawal: x ray pulsars in x ray binaries are bright x ray sources, in fact they are beighter than magnetors when magnetors are not in state of outbursts the radio pulsars are rotating neutru stars which generalyy have lowere magentic field typically 10^9 gauss, the x ray pulsars are accreting neutron stars in binary syystems and have high magnetic field about 10^13 to 10^13 gauss thus x ray pulsars are powered b release of gravitational energy by the accreting matter while the radio pulsars are powered by rotational energy of neutron stars. Majority of radio pulsars are single neutron stars

salonibhatiaini17: possibility of binary magnetars?

Prof. Agrawal: so far we have not detedted binary magnetars, that means two magnetars in a binary system

salonibhatiaini17: it should be very bright

Rathnasree: Thanks for being there everyone, This is the end of the chat. Hope to see you all in the next lecture in this series

Link to the Youtube lecture segments of the lecture on X-Ray Astronomy by Prof. P. C. Agrawal

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Page last modified on June 27, 2010, at 01:14 PM EST