h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

" some of the objects we see when we look into the night sky have long since reached the ends of their lives." Which ones?
How do you know?
No doubt stars have gone nova in 15 billion years.
But galaxies look eternal to me , until they collide!
Then the remants make another bigger galaxy

Hi johninf,

We know this because we know how long different kinds of objects live for. We know, for example, that stars like our Sun live for about 10 billion years. Our Sun is currently about 5 billion years old, so it will continue to burn for approximately another 5 billion years. We know this because we understand the process of energy that produces the light we see, and we know how much fuel the Sun has because we know how heavy it is. Heavier stars have much shorter lifetimes. Similar reasoning holds for other kinds of objects. By applying physics we get an understanding of how they work, and can then estimate how long they will last for. If the projected lifetime is shorter than the light travel time to the object, then it is likely that the object no longer exists in the form we see it.

Galaxies are largely made up of stars, gas and dust, as well as more exotic objects like black holes. Galaxies themselves are very long-lived objects, but they will only continue as they are for as long as there is gas available to make new stars as the old ones die. Collisions do not always destroy the galaxies involved. Astronomers have found convincing evidence that suggests our Galaxy has collided with several other, much smaller, galaxies in the past.

Megan

I think the universe is infinite, and that galaxies
are eternal.
However to reply......... In agree no body would lkke to
estimate the lifetime of a galaxy.
I would like to se evidence that the milky way has collided with other galaxies bit I will believe it. I think we will collide with Andromeda ptetty soon its blue shifting.
"Galaxies themselves are very long-lived objects, but they will only continue as they are for as long as there is gas available to make new stars as the old ones die."
When stars go nova they produce masses of gas and dust
like nebula, in which new stars can be born.
I like Fred hoyle, this book was published in 2001,
just after or before he died still passionately disblieving the big bang. An expression he invented ! !

It proposes little big bangs extemely interesting.
Hope you will read and send me your comments.

Astrophysics, abstract
astro-ph/0108051
From: John A. Tomsick [view email]
Date: Thu, 2 Aug 2001 23:18:49 GMT (12kb)

Quasi-Steady State Cosmology
Authors: G. Burbidge (UCSD)
Comments: 14 pages, in Proceedings of Frontiers of the Universe Conference, 17-23 June 2001, in press

A brief historical account of modern cosmology shows that the standard big bang (BB) model, believed by so many, does not have the strong observational foundations that are frequently claimed for it. The theory of the Quasi-Steady State Cosmology (QSSC) and explosive cosmogony is outlined. Comparisons are made between the two theories in explaining the observed properties of the universe, namely, the expansion, chemical composition, CMB, QSO redshifts and explosive events, galaxy formation, and the m-z and theta-z relations. Only two of the observed properties have ever been predicted from the theories (a) the expansion predicted from Einstein's theory by Friedmann and Lemaitre, and (b) the acceleration predicted by the classical steady state theory and the QSSC.
Full-text: PostScript, PDF, or Other formats

Indeed their are various authors who are presenting evidence which tends to disprove the "Big Bang " theory, or at least provide interesting theories which seem to account for the observations better than the dominant paradigm. Eric Lerner's _The Big Bang Never Happened_, and Halton Arp's _Seeing Red_ are just two of the more thoughtful books on the subject. Halton Arp especially conveys the frustration inherent in trying to present unwelcome observational data.

Marshall_R.

Yes, there are debates over it - that's the nature of science. All we can say is that the Big Bang is the current preferred theory. If evidence is found that does not match the predictions of the Big Bang theory, then scientists will *have* to modify the theory, that's the way science works! When it was first suggested the idea wasn't taken seriously. Remember: we've only known about redshift of galaxies since Hubble's work, and we've only known that galaxies are outside the Milky Way for a relatively short time (in the history of astronomy). Astronomy has come a long way in the last hundred or so years, but we're still a long way from knowing all the answers (and isn't that exciting?! )