WISE reveals the X-shaped bulge of our galaxy

March 3, 2016 by Tomasz Nowakowski report
The WISE W1 and W2 image fit by a simple exponential disk model, making the X structure more apparent. Top-left: Data. Top-middle: Data, masking out the top and bottom 5 percent of pixels based on W1 − W2 color, as well as pixels with negative flux. The diagonal structure at the top of the image is due to scattered light from the Moon in the unWISE coadds. Top-right: Exponential disk model fit. Bottom-left: Residuals (data minus model). Bottom-middle: Masked residuals. Bottom-right: 50-pixel median filter of masked residuals (median of unmasked pixels). Credit: Melissa Ness/Dustin Lang, 2016.

Using a set of coadded images taken by NASA's Wide-field Infrared Survey Explorer (WISE), astronomers from the Max Planck Institute for Astronomy in Germany and the University of Toronto in Canada, have provided new insights on the morphology and structure of the bulge of our home galaxy, the Milky Way. They revealed the X-shaped nature of the bulge, which could have important implications for the understanding of the formation history of our galaxy. The findings are presented in a research paper published online on Feb. 29 on the arXiv server.

WISE is an infrared-wavelength astronomical space telescope launched in December 2009 that completed a full sky photometric survey using four bands in the mid-infrared at 3.4, 4.6, 12 and 22 μm wavelength range bands over 10 months. It scanned the entire sky twice, snapping pictures of nearly billion objects, including remote galaxies, stars and asteroids. Data from WISE has been released to the public and include processed, contrast-enhanced pictures grouped in a catalog called "unWISE." This set offers coadded images using enhancement technology that does not degrade the resolution of the photo.

Melissa Ness and Dustin Lang, the paper's co-authors, claim that the Milky Way is irrefutably morphologically X-shaped. According to the paper, this peculiar shape was revealed by the 'split in the red clump' from star counts along the line of sight toward the bulge. When the scientists studied contrast enhanced, zoomed-in versions of the images provided by WISE, they spotted the X-shaped light profile of the bulge and its extent across the photo.

"No additional unsharp masking or equivalent techniques have been used to enhance these data. The bulge in the central region shows a clear X-shaped morphology," the researchers wrote in the paper.

By looking at the images from the "unWISE" catalog, they found that the arms of the X-shaped feature are asymmetrical around the minor axis and appear larger at left than at right. The bulge is oriented at about 27 degrees with respect to the line of sight, with the nearest side at positive longitudes.

Previous studies have questioned the X-shaped nature of this feature, arguing that the 'split in the red clump' may be due to different stellar populations, in an old classical spheroidal bulge. Now, the new findings confirm this peculiar shape, similar to that seen in the unsharp masked images of other barred spiral galaxies.

The spatial mapping presented in the research could provide a useful guide for current and future spectroscopic surveys such as APOGEE (APO Galactic Evolution Experiment), slated to map over 100,000 red giant stars across the full range of the Milky Way's galactic bulge, bar, disk, and halo. It could be also helpful for bulge programs associated with the GALactic Archaeology with HERMES (GALAH) survey, an ambitious project to observe a million stars in our galaxy.

"These data can be used to guide stellar target selection, where examining the spectroscopic ages and metallicities of stars in the arms of the X-shape will be necessary to understand the formation of the bulge and constrain the formation processes relevant in the Milky Way," the astronomers concluded.

Explore further: Starry surprise in the bulge: encounter of a halo passerby

More information: arxiv.org/pdf/1603.00026.pdf

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cantdrive85
2 / 5 (8) Mar 03, 2016
That would be the evidence of the z-pinched Galactic Birkeland current.
Tuxford
3.4 / 5 (5) Mar 03, 2016
Just looking at the conical ejection pattern from the core, similar in form to Fermi Bubbles.
Protoplasmix
3.3 / 5 (7) Mar 03, 2016
That would be the evidence of the z-pinched Galactic Birkeland current.
Don't you mean "x-pinched"? c'mon cantdoaybeeseezeither
OdinsAcolyte
not rated yet Mar 04, 2016
A barred galaxy with an x shape central bulge.
Interesting things happening at the galactic core..
OdinsAcolyte
not rated yet Mar 04, 2016
A barred galaxy with an x shape central bulge.
Interesting things happening at the galactic core..
RealityCheck
3.7 / 5 (3) Mar 04, 2016
Hi all. :)

Didn't astronomers recently discover galactic scale magnetic field torus pattern around/through stellar/ionized dust/gas material of accretion disc?

So observed light pattern is result of out-curving conical radiation pattern.

One source of radiation is synchrotron radiation from charged particles from galactic 'ion winds' escaping from galaxy core region via poles (much less blocking gas/dust material there than in disk plane) and being accelerated by stronger magnetic fields concentrating at inner torus. Another radiation component maybe from stellar/other processes (which gave rise to the ionized winds material) radiating out into the less opaque respective hemispheres via respective polar regions.

What we see as "X" pattern of radiation is 'radiation density artifact' of tangential denser cross-section view through either side of the respective polar radiation cones.

If there were strong Active Galactic Nucleus polar jets, it'd look different. Cheers. :)
Protoplasmix
4 / 5 (8) Mar 05, 2016
Didn't astronomers recently discover galactic scale magnetic field torus pattern around/through stellar/ionized dust/gas material of accretion disc? … [more nonsense about dust, radiation, and toroidal magnetic fields] ...
Well, RealityCheck, you clearly didn't even bother to check the reality of what astronomers concluded from these observations and from observations of other barred spiral galaxies.

From the paper: "The W3 and W4 bands largely trace dust rather than stellar light and therefore do not reveal the X-shaped profile."

So, the light that forms the X-structure is from stars, and astronomers have "determined their distribution to be characteristic of a strong boxy/peanut bulge in a barred galaxy." This is similar to what's observed in other barred spiral galaxies, and it is not 'polar radiation cones.' I thought you were smarter than the electric idiots, RC.
cavemmxv
not rated yet Mar 05, 2016
I may be an idiot too but sure looks like the pattern associated with the precession of a spinning gyro.
Black holes do spin, right?
RealityCheck
2.6 / 5 (5) Mar 05, 2016
Hi Protoplasmix. :)
Well, RealityCheck, ...From the paper: "The W3 and W4 bands largely trace dust rather than stellar light and therefore do not reveal the X-shaped profile."

So, the light that forms the X-structure is from stars,...
Did you miss this in my post?...
Another radiation component maybe from STELLAR/other processes (which gave rise to the ionized winds material) radiating out into the less opaque respective hemispheres via respective polar regions.
See? I also mentioned known physics of what is also happening in that region; which includes synchrotron radiation from magnetically accelerated particles, and re-radiation from the ionized dust/gas in the galactic winds from those regions into the respective hemispheres.
I thought you were smarter than the electric idiots, RC.
Why bring EU into it? Galactic scale magnetic torus patterns in spiral galaxies is a MAINSTREAM DISCOVERY. Aren't you aware of that? Keep EU diversions out of this, ma
gkam
1 / 5 (3) Mar 06, 2016
" I thought you were smarter than the electric idiots, RC."
-----------------------------

Can we get rid of the barbarism in this forum? These folk who hide behind phony names think they can take out their frustrations of their pathetic lives on others.

Please grow up, protowhatever you think you are.
cantdrive85
1 / 5 (3) Mar 06, 2016
" I thought you were smarter than the electric idiots, RC."
-----------------------------

Can we get rid of the barbarism in this forum? These folk who hide behind phony names think they can take out their frustrations of their pathetic lives on others.

Please grow up, protowhatever you think you are.

It makes her feel better about herself, typical Cro-Mag behavior. The irony is that her world view requires fairy dust and unicorns to explain reality, it's a "proto-reality" from a diminutive cranial primitive type.
TheGhostofOtto1923
5 / 5 (2) Mar 08, 2016
hide behind phony names think they can take out their frustrations of their pathetic lives on others
George kamburoff the apparent psychopath thinks that hiding behind his real name gives him the right to post outrageous bullshit like this:
Fallout is the main cause of lung cancer

HIGH ENERGY alpha cannot penetrate skin

Swimming pools are routinely used to provide residential cooling

There was an H2-initiated prompt criticality in dirty molten Pu at fukushima which mustve occured somewhere high above the site because a crater wasnt created

Manure dust is called volatile solids and is a main constituent of pollution in the 'high air' above the central valley

It is ok for george to double the number and intensity of earthquakes in a region on a given day because he has actually experienced them before

Pu is raining down on idaho
-without being questioned.

George kamburoff what questions would potential employers have after reading the insanity you post?

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