Gotta love oddball objects – they’re the poles holding up the tent of common phenomenon. This one, from NewScientist (1 April 2017), caught my eye:
When small stars perish, they expand and create glowing shells of ionised gas, called planetary nebulae. But when astronomers observed the Boomerang Nebula in 1995, they saw something quite odd. It’s the only known object in the universe to absorb light from the cosmic microwave background (CMB) – the afterglow of the big bang that keeps the universe 2.7 degrees above absolute zero. That means the nebula must be even colder.
Expanding gases will cool, but no one knew how Boomerang’s central star could eject enough gas to cool it to the temperature we see now in so short a time. …
[Using the Atacama Large Millimeter/submillimeter Array,] we have the first detailed map of the Boomerang. On large scales, at least 3.3 times as much mass as the sun contains is being swept away from the central star at 170 kilometres per second within a spherical shell of gas. Could a single star produce such an outburst? [Raghvendra Sahai of JPL] didn’t think so.
ALMA’s high resolution let the team probe the frigid heart of the system as well. It turns out that within the shell of gas two smaller bubbles are expanding outward from the central star.
The team suggests that the single star was actually two, with one much larger than the other. When the massive star died and started to swell, it swallowed the smaller one. The companion continued to orbit the primary star’s core within the shell of gas. Eventually, it spiralled into the core roughly 1000 years ago in a violent merger that disgorged the two smaller lobes of gas (arxiv.org/abs/1703.06929).
Fascinating – you think of cosmic explosions as a location of heat, not cold. Elsewhere, they state that temperature appears to be 0.1 kelvin.
Boomerang Nebula. Image: NASA, ESA and The Hubble Heritage Team (STScI/AURA)
A couple of years ago, SciNews published early results concerning the Nebula’s shape:
[Sahai’s] group discovered a dense lane of millimeter-sized dust grains surrounding the nebula’s central star, which explains why the outer cloud has an hourglass shape in visible light. The dust grains have created a mask that shades a portion of the central star and allows its light to leak out only in narrow but opposite directions into the cloud, giving it an hourglass appearance.
