“Necklace” planetary nebula PN G054.2-03.4 in Sagitta

Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

The “Necklace Nebula,” also called PN G054.2-03.4, is the exploded aftermath of a giant star that came too close to its Sun-like binary companion. The two stars that produced the Necklace Nebula live in a relatively small orbit about each other. They have a period of 1.2 days and a separation on the order of 5 times the radius of the Sun. Evidence for the existence of the two-body system arises from the nebula’s appearance of a half-light-year-wide equatorial ring of dense material near the inner portion of the nebula. The expanding elliptical ring is composed of bright, dense knots of glowing hydrogen and oxygen gas. Each knot also dons a small tail pointing away from the central star. The clumpy appearance of the ring may have been caused by density fluctuations in the shared material of the binary stars prior to the explosion, or possibly by magnetic field lines present in the giant star as it began to expand and shed off its outer layers.

A fast, collimated outflow of nitrogen gas from the binary system has formed faint lobes and polar caps extending in the direction perpendicular to the ring. Edge to edge, the nebula is nearly 9 light-years long, over twice the distance between our Sun and our nearest stellar companion, Proxima Centauri. Astronomers studying PN G054.2-03.4 predict that the outer lobes of gas were ejected about 10,000 years ago, before the two stars began sharing material. The inner ring of material was created only about 5,000 years ago (and relatively recent on astronomical timescales), and shares the same plane as the orbit of the two stars. The Necklace Nebula is located about 15,000 light-years away in the northern constellation Sagitta. It was recently discovered in 2005 from the Isaac Newton Telescope Photometric H-alpha Survey (IPHAS), a ground-based H-alpha planetary nebula study of the North Galactic Plane.

Update: The first ground-based imaging detection of an exoplanet in the optical (wavelength less than one micron) is β Pic b reported today using the Magellan and Gemini telescopes. Another new study has investigated low mass stellar members of the 40 Myr Tucana-Horologium moving group.


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: