Infrared Stellar Mystery Solved With Magnetic Fuzz
Artist impression of the magnetic loops carring gas and dust above disks of planet-forming material circling stars, creating a protoplanetary 'sunset.'
NASA/JPL-Caltech/K. Su (Univ. of Arizona)
NASA's Spitzer Space Telescope was launched 10 years ago and has since peeled back an infrared veil on the Cosmos. The mission has worked in parallel with NASA's other "Great Observatories" (Hubble and Chandra) to provide coverage of the emissions from galaxies, interstellar dust, comet tails and the solar system's planets. But some of the most striking imagery to come from the orbiting telescope has been that of nebulae. Supernova remnants, star-forming regions and planetary nebulae are some of the most iconic objects to be spotted by Spitzer. So, to celebrate a decade in space, here are Discovery News' favorite Spitzer nebulae.
First up, the Helix Nebula -- a so-called planetary nebula -- located around 700 light-years from Earth. A planetary nebula is the remnants of the death throes of a red giant star -- all that remains is a white dwarf star in the core, clouded by cometary dust.
NASA/JPL-Caltech/B. Williams (NCSU)
Spitzer will often work in tandem with other space telescopes to image a broad spectrum of light from celestial objects. Here, the supernova remnant RCW 86 is imaged by NASA's Spitzer, WISE and Chandra, and ESA's XMM-Newton.
Staring deep into the Messier 78 star-forming nebula, Spitzer sees the infrared glow of baby stars blasting cavities into the cool nebulous gas and dust.
The green-glowing infrared ring of the nebula RCW 120 is caused by tiny dust grains called polycyclic aromatic hydrocarbons -- the bubble is being shaped by the powerful stellar winds emanating from the central massive O-type star.
NASA/JPL-Caltech/J. Stauffer (SSC/Caltech)
Spitzer stares deep into the Orion nebula, imaging the infrared light generated by a star factory.
X-Ray: NASA/CXC/J.Hester (ASU); Optical: NASA/ESA/J.Hester & A.Loll (ASU); Infrared: NASA/JPL-Caltech/R.Gehrz (Univ. Minn.)
In the year 1054 A.D. a star exploded as a supernova. Today, Spitzer was helped by NASA's other "Great Observatories" (Hubble and Chandra) to image the nebula that remains. The Crab Nebula is the result; a vast cloud of gas and dust with a spinning pulsar in the center.
The Tycho supernova remnant as imaged by Spitzer (in infrared wavelengths) and Chandra (X-rays). The supernova's powerful shockwave is visible as the outer blue shell, emitting X-rays.
NASA/JPL-Caltech/E. Churchwell (University of Wisconsin - Madison)
Over 2,200 baby stars can be seen inside the bustling star-forming region RCW 49.
X-ray: NASA/CXC/Univ.Potsdam/L.Oskinova et al; Optical: NASA/STScI; Infrared: NASA/JPL-Caltech
The "Wing" of the Small Magellanic Cloud (SMC) glitters with stars and warm clouds of dust and gas. By combining observations by Spitzer, Chandra and Hubble, the complex nature of this nebulous region can be realized.
NASA’s Spitzer Space Telescope has helped solve an infrared mystery surrounding baby star systems that has puzzled astronomers since the 1980s.
A star is born from the gravitational collapse of clouds of dust and gas. When the compressed star-forming cloud reaches a certain density, fusion reactions are triggered in the core — a young star is born. However, during this collapse, there is a natural rotation in the cloud, a rotation that is preserved by the star as it reaches maturity. Any leftovers from the stellar formation accumulates around the new star forming a spinning, flat protoplanetary disk that creates rocky bodies like asteroids and eventually planets.
During the 1980s, the Infrared Astronomical Satellite (IRAS) mission surveyed young star systems measuring the infrared light they emitted. The protoplanetary disk of gas and dust generates a strong infrared signal — the young star heats up the disk, which radiates in infrared wavelengths.
However, even during those early observations, astronomers noticed a discrepancy; the young star systems were generating too much infrared radiation.
Over the years, further infrared observations and more refined models have suggested that the simple “flat” structure of protoplanetary disks may need to be revisited. Revised theoretical models included a modification of the ‘classic’ protoplanetary disk, adding a halo of dusty material encapsulating the young, hot star. By doing this, more dust is heated than the disk scenario and could perhaps explain the excess in infrared radiation.
However, with the help of Spitzer and new 3-D models, astronomers think they have a more refined answer.
As the star-forming cloud collapses, the new star not only retains the angular momentum of the spinning cloud, it also collapses any magnetic fields contained within it. The magnetic field will thread through the protoplanetary disk creating huge loops, trapping gas, dust and plasma, enhancing the disk’s atmosphere. These huge arcs — like the bright coronal loops that are filled with hot plasma reaching high above the sun’s photosphere — could be what is responsible for the excess; starlight is blocked by the huge arcs, which are then heated to generate more infrared radiation.
“If you could somehow stand on one of these planet-forming disks and look at the star in the center through the disk atmosphere, you would see what looks like a sunset,” said Neal Turner of NASA’s Jet Propulsion Laboratory, Pasadena, Calif. The disk, in this case, is not smooth or flat — the magnetic fields crate a fuzziness, forcing the starlight to heat more dust.
“The starlight-intercepting material lies not in a halo, and not in a traditional disk either, but in a disk atmosphere supported by magnetic fields,” said Turner. “Such magnetized atmospheres were predicted to form as the disk drives gas inward to crash onto the growing star.”
Astronomers now hope to continue refining this model by observing more protoplanetary systems with observatories like NASA’s SOFIA telescope, the Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile and NASA’s James Webb Space Telescope.