Astronomy

[Dreamwoven]

That link of yours, prendrelemick, was very interesting and useful. I learned a lot about the life of stars from it - and, of course, about their death in a gigantic thermonuclear explosion.

[YesNo]

I didn't realize that a nova happened in a binary star system with one of the stars being a white dwarf. It looks like it is an explosion of two stars.

[Dreamwoven]

http://earthsky.org/space/cassini-be...year-at-saturn

[prendrelemick]

I hadn't heard of quark stars either, but they would be some way to put more mass into a neutron star without completely collapsing it to a black hole point. It is that collapsing to a point that puzzles me. If the escape velocity from the surface of the object is the speed of light does that mean that the "surface" must be an "event horizon" and no longer a surface?

Apparently Moffat has a way out of needing black holes, but I haven't read enough of the book to know what it is.

Although I have an account on the physics stack exchange, I have only posted items on the math stack exchange and that only after discussing number theory with desiresjab.

Perhaps we could try and understand that escape velocity equation that is on your link. I'm not sure what the terms are (never mind the units) is R for radius, v for velocity, m for mass G for ? I notice everything on one side is divided by R so the smaller it gets the bigger the value. I presume that it represents the inverse square rule - Does that mean that if you halve R, V is squared? As you may now realize I know nothing of maths.

EDIT: Reading on further it seems once the escape velocity of the object approaches the speed of light, collapse must continue to a singularity as it can no longer hold itself up. The author also told us not to think about it too much! Look at the equation for the Schwartzchild radius - can it be equal to the radius of the actual object?

That link of yours, prendrelemick, was very interesting and useful. I learned a lot about the life of stars from it - and, of course, about their death in a gigantic thermonuclear explosion.

Yes it was good for that, but the stuff about string theory made me wonder how reliable it was even though the caveat "perhaps" was used. Isn't String Theory is going out of fashion at the moment. What really struck me was the miniscule size of the strings.

[Dreamwoven]

http://earthsky.org/space/cassini-be...year-at-saturn

Saturn is a fascinating Ice Giant and I look forward to the final year as Cassini plunges down for a closer look.

[prendrelemick]

I can't believe it has been up there since 2004. The video makes no mention of the different coloured regions on the planet's "surface" I wonder where abouts they are going to crash it.

[YesNo]

Perhaps we could try and understand that escape velocity equation that is on your link. I'm not sure what the terms are (never mind the units) is R for radius, v for velocity, m for mass G for ? I notice everything on one side is divided by R so the smaller it gets the bigger the value. I presume that it represents the inverse square rule - Does that mean that if you halve R, V is squared? As you may now realize I know nothing of maths.

EDIT: Reading on further it seems once the escape velocity of the object approaches the speed of light, collapse must continue to a singularity as it can no longer hold itself up. The author also told us not to think about it too much! Look at the equation for the Schwartzchild radius - can it be equal to the radius of the actual object?

G would be the gravitational constant: https://en.wikipedia.org/wiki/Gravitational_constant

There is some question in that article about whether it is a constant like pi, unchanging for infinitely many decimal places. I assume a physical constant must break down at some point, but maybe those gravitational wave instruments will be able to get good measurements of it. If it does change, then an explanation for that change would be needed.

From reading Moffat, there are three kinds of postulated black holes: mini black holes, black holes from solar collapse and large black holes at the center of galaxies. The evidence for their existence comes from measuring the motions of objects around them and calculating how much mass would be needed to keep those motions going and then assuming it is caused by a black hole since the mass is too large to be a neutron (or quark) star.

However, a prediction that a cloud would fall into the black hole at the center of our galaxy didn't happen last year: https://en.wikipedia.org/wiki/Sagitt...cretion_course

That makes me question whether there is a black hole at the radio source Sgr A*.

[Dreamwoven]

http://www.universetoday.com/131081/...ive-shrinking/

The Messenger probe sent by NASA has been investigating this hitherto little known innermost planet. A landing probe is to be sent there to investigate further.

[Dreamwoven]

I didn't even know that a probe was sent to Mercury, nor that further investigations by a second probe will be taking place.

[YesNo]

I didn't know Mercury was an active planet. Also being "active" appears to mean it is "contracting". I previously thought that just meant the surface was moving around because of internal heat. Perhaps the Sun also provides some of the energy to keep the planet active.

[Dreamwoven]

When you think about it, NASA has worked wonders in exploring the solar system. From vehicles on Mars, to exploring every planet and dwarf planet its an accomplishment that has hugely enriched our lives.

[prendrelemick]

Meanwhile today, the Rosetta probe is going to be crashed into comet 67p they are hoping to get 4 closeup pictures, but the slow data transfer might be a problem. The Comet is thought to have the consistancy of frozen cigarette ash, so crash might be the wrong word.

[Dreamwoven]

The European Space Agency is a co-operative project between a number of European states (it is separate from the European Union and is funded by European states directly). It is a much more modest affair than NASA, but has achieved surprisingly good results considering its limited budget. The James Webb Space Telescope is its latest development due to be launched in 2018.

[YesNo]

Maybe the Rosetta probe will just fall through the comet? In that case, I hope it survives to continue sending data after the crash.

[Dreamwoven]

http://www.universetoday.com/130961/...ns-discovered/

There are thousands of satellites captured by Jupiter that have been identified and named to date. The large ones are called Jupiter Trojans and can be up to 200km in diameter and more are being discovered all the time. The article above from universe today discusses this in the context of the University of Taiwan's work on Trojans from observations by the Pan-STARRS telescopes on Hawaii.

This work has been going on for some time but is still in its early stages and there are also many satellites of the Ice Giants in orbit round the sun - Neptune and Uranus. We know very little about these, just from Voyager flybys in the 1980s. Just identifying and counting the satellites is going to be a problem, we know even less about the other gas giant, Saturn. These will probably have to be visited by their own probes, just as has been with Juno.

All this is just to show how little we know about the large outer planets. And if there is a ninth giant planet that makes another to add to the total.