Free Astronomy Magazine November-December 2015

SPACE CHRONICLES New Hubble image of the Twin Jet Nebula by NASA T he cosmic butterfly pictured in this NASA/ESA Hubble Space Telescope image goes by many names. It is called the Twin Jet Neb- ula as well as answering to the slight- ly less poetic name of PN M2-9. The M in this name refers to Rud- olph Minkowski, a German-Ameri- can astronomer who discovered the nebula in 1947. The PN, meanwhile, refers to the fact that M2-9 is a plan- etary nebula. The glowing and ex- panding shells of gas clearly visible in this image represent the final sta- ges of life for an old star of low to intermediate mass. The star has not only ejected its outer layers, but the exposed remnant core is now illumi- nating these layers — resulting in a spectacular light show like the one seen here. However, the Twin Jet Ne- bula is not just any planetary nebula, it is a bipolar nebula. Ordinary pla- netary nebulae have one star at their centre, bipolar nebulae have two, in T he Twin Jet Nebula, or PN M2-9, is a striking example of a bipolar planetary nebula. Bipo- lar planetary nebulae are formed when the central object is not a single star, but a binary system. Studies have shown that the nebula’s size increases with time, and measurements of this rate of increase suggest that the stellar outburst that formed the lobes occurred just 1200 years ago. [ESA/Hubble & NASA] a binary star system. Astronomers have found that the two stars in this pair each have around the same mass as the Sun, ranging from 0.6 to 1.0 solar masses for the smaller star, and from 1.0 to 1.4 solar masses for its larger companion. The larger star is approaching the end of its days and