In simplest terms, what is null dust?

[nomadreid]

The links I pull up assume that the reader knows what null dust is. Which I don't. An explanation would be appreciated.
The question came up when looking for an (equally absent) clear explanation of Vaidya spacetime.
This, in turn, came up while looking at the article http://prola.aps.org/abstract/PRD/v70/i10/e101502; perhaps also could someone tell me whether this is just a rerun of the outmoded "white hole" construction?

[George Jones]

Null dust is a pressureless fluid (the dust part) that has lightlike streamlines (the null part).

For the Vaidya spacetime, take a look at sections 4.3.5 and 5.1.8 in Eric Poisson's notes,

http://www.physics.uoguelph.ca/poisson/research/agr.pdf.

Better yet, see if your library has a copy of the excellent book, A Relativist's Toolkit: The Mathematics of Black Hole Mechanics, into which the notes evolved.

Your prola link doesn't work, and I have access to prola. Can you find an arXiv link?

[cristo]

Your prola link doesn't work, and I have access to prola. Can you find an arXiv link?

There's a stray semicolon at the end of that link. The correct one is: http://prola.aps.org/abstract/PRD/v70/i10/e101502

[nomadreid]

Thanks, George Jones and Christo.
George Jones: I have downloaded the Poisson book on GR, and will be looking working through the sections you mentioned. Thank you for your book recommendation, but I presently have no access to a decent academic library. Christo answered about the link.

[George Jones]

is just a rerun of the outmoded "white hole" construction?

No. A wormhole need exotic stuff to hold it open, and this example uses radiation with negative energy density.

arXiv link:

http://arxiv.org/abs/gr-qc/0406080.