Letters from the February 9, 2008, issue of Science News

Small, or just invisible?

“Heavy Find: Weighty neutron stars may rule out exotic core” (SN: 1/12/08, p. 20) says that the companion star of the pulsar PSR B1516+02B must be “tiny” because it cannot be seen. Isn’t it possible that the companion is made of dark matter? Is there a “wobble” test or other way to discern between a companion that is truly tiny (low mass) and one that is perhaps more massive but not visible? The mass of the companion star seems to bear directly on the conclusion favoring heavy neutron stars.

Maureen McAllister
Wayne, Ill.

The companion to PSR B1516+02B is very likely a white dwarf star, says Paulo Freire of Arecibo Observatory in Puerto Rico. White dwarfs are faint, and become harder to detect as they grow older and cooler. Few companions to millisecond pulsars have ever been directly detected, but those that have are almost all white dwarfs. Freire adds that dark matter seems to clump at galactic scales, and that he is not aware of any theoretical predictions of dark matter able to form small objects like stars.—Ron Cowen

Defining ‘pristine’

“Prairie Revival: Researchers put restoration to the test” (SN: 12/15/07, p. 376) talks of restoring prairies to an earlier state, but if the concepts summarized in Charles C. Mann’s book 1491: New Revelations of the Americas Before Columbus are even within shouting distance of reality, the “native prairie” being pursued by some represents a fleeting moment in time created by the destruction of a civilization and the total collapse of its agricultural support system. The “pristine” environment concept, both in the prairies and in the rainforests, may well be wrong.

Lon Crosby
Webster City, Iowa

Most researchers acknowledge that restoring a prairie to a state free of human intervention is impossible. The prairie landscape itself was created by fire and grazing, processes that Native Americans manipulated. Understanding how that landscape was maintained is an active area of study and re-implementing those processes is a cornerstone of prairie restoration.—Leslie Allen