Other news topics
	Resource Topics
	Earth, Moon, and the Sun  The Solar System  Space Probes and Human Exploration  Stars and Nebulae  Astronomers and Observatories  Galaxies and Cosmology  Stargazing and Star Lore
	Resources
	FAQs about Galaxies and Cosmology
	Astronomy Gift Shop
	2008 Sky Almanac Pentax 10x50 binoculars McDonald Observatory logo cap

Orbiting observatories have discovered what may be a new class of stars. Called “quark” stars, these objects are squeezed so tightly by their immense gravity that protons and neutrons break down into their component particles, called quarks.

When a star dies, gravity crushes its core. The density of this stellar corpse depends on the star’s original mass. A star as massive as our Sun becomes a white dwarf, which is about as big as Earth. Stars a few times heavier than Earth leave neutron-star remnants, which are about the size of a city. And the cores of heavier stars are crushed so tightly that they become black holes.

A quark star may represent an intermediate step between neutron stars and black holes — smaller and denser than a neutron star, but not dense enough to become a black hole. The orbiting Chandra X-Ray Observatory and Hubble Space Telescope found evidence of two quark stars.

One is known by the catalog designation RX J1856.5-3754 (the numbers represent its position in space). By combining observations from both observatories, a team of astronomers led by Jeremy Drake of the Harvard-Smithsonian Center for Astrophysics (CfA) found that it radiates energy into space like a solid body with a temperature of 1.2 million degrees Fahrenheit (700,000 C). They also found that the star is about seven miles (11.3 km) in diameter. Neutron stars should be no smaller than about 10 miles (16 km) in diameter, so the observations indicate that RX J1856 is a denser type of star: a quark star.

Astronomers note, however, that RX J1856 could be a neutron star with an unusually hot region on its surface. And a report by another astronomer suggests that estimates of the star’s distance from Earth may be incorrect, throwing off the measurements of its temperature and size. The other system, 3C58, is cooler than expected. Astronomers Patrick Slane and Steven Murray of CfA, and David Helfand of Columbia University, measured the X-rays produced by the system, which astronomers believe is the remnant of a supernova explosion recorded by Chinese and Japanese astronomers in 1181. Slane’s team calculated that the star’s temperature is less than one million degrees Centigrade, which is far cooler than expected for a young neutron star. As with RX J1856, the team studying 3C58 concludes that a new form of matter — a quark star — may be required to explain their findings. DB