There's a Peanut in the Center of Our Galaxy
Artist's impression of the central bulge of the Milky Way -- from some angles, it looks like a peanut.
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.
By now, we're probably all aware that a supermassive black hole lurks in the center of our galaxy, approximately 27,000 light-years away. But I bet you didn't know that there's also a supermassive peanut hiding there too!
No, Sagittarius A* (Sgr A*) -- the radio emission that marks the location of our galaxy's black hole behemoth -- hasn't been caught snacking again, this peanut represents the shape of the central bulge after it was mapped by two groups of astronomers using publicly available data from the European Southern Observatory (ESO) VISTA survey telescope.
The central bulge of our galaxy contains around 10,000 million stars and spans thousands of light-years, but due to the obscuring dust and gas intermingled with this stellar hive, the overall shape of the bulge is poorly understood. Previous data from the Two Micron All Sky Survey (2MASS) project suggested the central galactic bulge was X-shaped -- in a similar fashion to other galaxies observed in the Universe.
But using high resolution infrared data from VISTA, a better idea of the bulge's shape has been mapped.
By focusing on 2 million red giant stars whose properties are well understood, very precise distances could be calculated. By doing this, a 3-dimensional model of the galactic bulge could be constructed.
"We find that the inner region of our Galaxy has the shape of a peanut in its shell from the side, and of a highly elongated bar from above", said Ortwin Gerhard, co-investigator and leader of the Dynamics Group at the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, Germany. "It is the first time that we can see this clearly in our own Milky Way, and simulations in our group and by others show that this shape is characteristic of a barred galaxy that started out as a pure disc of stars."
The second team of astronomers led by Sergio Vásquez, of the Pontificia Universidad Católica de Chile, Santiago, Chile, took a different approach to arrive at a similar conclusion. By comparing images of the central bulge 11 years apart using the MPG/ESO 2.2-metre telescope, tiny shifts due to the motions of the bulge stars across the sky were measured. This betrayed the shape of the bulge.
"The stars we have observed seem to be streaming along the arms of the X-shaped bulge as their orbits take them up and down and out of the plane of the Milky Way. It all fits very well with predictions from state-of-the-art models!" said Vásquez.
Both groups of astronomers believe that the center of the galaxy started out as a flat disk of stars, but over the aeons became buckled and warped, eventually settling into the modern day "peanut."