Letters from the May 19, 2007, issue of Science News

Merry go round

When considering a spin rate of 1,122 revolutions per second, has anyone determined the diameter of the neutron star XTE J1739-285 (“Dance of the dead,” SN: 3/17/07, p. 173)? If, for example, it were the same diameter as Earth, it would be traveling far in excess of the speed of light at its equator. In order to remain within the limitations of the speed of light its diameter would have to be less than a hundred miles!

R.G. Paul
Upland, Calif.

What is the maximum rate before the star flies apart from the rotation forces?

Sean Walton
Orem, Utah

The speed of light would limit the star to a 43-kilometer radius, says astronomer Phil Kaaret of the University of Iowa in Iowa City. He adds that there’s little surprise in that, since the expected radii of neutron stars are in the range of 10 to 20 km. The maximum rotation rate would be between 1,000 and 2,000 rotations per second, depending on the properties of the ultradense matter in the star, says Kaaret.—R. Cowen

Captcha gotcha

It is ironic that the article “Games Theory” (SN: 3/17/07, p. 170) describes a captcha [completely automated Turing test to tell computers and humans apart] and then goes on to demonstrate how to defeat it. An automated program that is supposed to pass this difficult computation test just has to forward the captcha image to a real person, at a different Web site, who will then unwittingly assist the automated program. The only challenge is to make it “fun” or otherwise compelling for the unwitting person.

John Haselsberger
Allentown, Pa.

Plant with caution

I find it absolutely incredible that anyone is seriously contemplating an escalation of “natural” herbicides (“Herbal Herbicides,” SN: 3/17/07, p. 167). As there is no “additive” sprayed on the crop, no testing is likely in animal or human clinical trials. We in the first world must bear the brunt of this wholesale testing on populations, as we have with so many other advances in agriculture and technology.

Carson Barnes
Loma Mar, Calif.