Milky Way's Fattening Behind Revealed
Hubble: NASA, ESA, and Q.D. Wang (University of Massachusetts, Amherst); Spitzer: NASA, Jet Propulsion Laboratory, and S. Stolovy (Spitzer Science Center/Caltech)
An infrared view of the center of our galaxy as imaged by NASA's Spitzer space telescope and the NASA/ESA Hubble Space Telescope.
NASA, ESA and the Hubble SM4 ERO Team
In a discovery announced on Sept. 4, 2013, a population of planetary nebulae near the galactic core appear to be, weirdly, preferentially aligned to the Milky Way's galactic plain. The nebulae, known as "bipolar" (or "butterfly") planetary nebulae are completely non-interacting and of various ages, suggesting some external force is shaping their orientation. It's thought that a powerful magnetic field may be the culprit.
The researchers used observations from the Hubble Space Telescope and ESO's New Technology Telescope, so here are a small selection of some stunning examples of bipolar planetary nebulae as seen through the eye of Hubble. Shown here is the stunning NGC 6302 -- an intricate example of a bipolar planetary nebula's butterfly wings.
Bruce Balick (University of Washington), Vincent Icke (Leiden University, The Netherlands), Garrelt Mellema (Stockholm University), and NASA/ESA
Hubble 5: A classically-shaped bipolar (or 'butterfly') planetary nebula.
ESA/Hubble & NASA
NGC 6881: A binary star possibly shapes this wonderfully symmetrical nebula.
NASA, ESA and the Hubble Heritage Team (STScI/AURA)
NGC 5189: A dramatic view of the ribbons of bright material being ejected from a planetary nebula.
Astronomers have long been in the dark about what is happening just beyond the center of the Milky Way. Stars in this region are mostly hidden by dust.
The only clue has come from measuring neutral hydrogen, an indirect technique that fed computer models showing the Milky Way’s outer disk is flared.
Now, a new study adds meat to the theory with the discovery of five relatively young, pulsating stars, known as Cepheid variables in the region of the suspected flare. Cepheids' regular pulsations and well-measured changes in brightness make them good yardsticks to measure astronomical distances.
The telltale stars were found 80,000 light-years from Earth beyond the galactic center, far above and below the Milky Way's plane.
“The presence of these relatively young -- less than 130 million years old -- stars so far from the galactic plane is puzzling, unless they're in the flared outer disk,” astronomer Michael Feast, with the University of Cape Town wrote in a paper published in this week’s Nature.
“We found the Cepheids at exactly the distance predicted for this increase in disk thickness,” Feast wrote.
Scientists don’t know exactly why the galaxy’s outer disk is fattening.
The thickening may be because there is less mass there to gravitationally corral the gas and stars into a flatter shape, such as what exists near the sun, astronomer Patricia Whitelock, with the South African Astronomical Observatory, wrote in an email to Discovery News.
“It is complex because one needs to take into account both the mass we observe -- such as the stars and gas -- and the dark matter which we only detect via its influence on the stars. Much more theoretical and observational work would be required to confirm this, or look for alternatives,” Whitelock said.
Scientists initially thought the Cephids, which were among a long list of potential variable stars in the direction of the galactic center, belonged to a neighbor galaxy, the Sagittarius Dwarf, which is in the process of merging with the Milky Way. Observations proved otherwise.
"We had to had to look for an alternative explanation,” Whitelock said.
More evidence may come from Europe’s Gaia spacecraft, which was launched in December to create three-dimensional maps of a billion stars and other objects in the Milky Way.
“It would be very interesting to identify large numbers of any well-understood stars at known distance, with their motion so that we could map out the distribution of mass in the galaxy,” Whitelock said.