Media Releases

X Marks the Spot at the Centre of the Milky Way Galaxy

July 19, 2016

Toron­to, ON – Two astronomers — with the help of Twit­ter — have uncov­ered the strongest evi­dence yet that an enor­mous X‑shaped struc­ture made of stars lies with­in the cen­tral bulge of the Milky Way Galaxy.

Pre­vi­ous com­put­er mod­els, obser­va­tions of oth­er galax­ies, and obser­va­tions of our own galaxy have sug­gest­ed that the X‑shaped struc­ture exist­ed. But no one had observed it direct­ly; and some astronomers argued that pre­vi­ous research that point­ed indi­rect­ly to the exis­tence of the X could be explained in oth­er ways.

“There was con­tro­ver­sy about whether the X‑shaped struc­ture exist­ed,” says Dustin Lang, a Research Asso­ciate at the Dun­lap Insti­tute for Astron­o­my & Astro­physics, Uni­ver­si­ty of Toron­to, and co-author of the paper describ­ing the dis­cov­ery. “But our paper gives a good view of the core of our own galaxy. I think it has pro­vid­ed pret­ty good evi­dence for the exis­tence of the X‑shaped struc­ture.”

The results appear in the July issue of theAstro­nom­i­cal Jour­nal. The lead author is Melis­sa Ness, a post­doc­tor­al researcher at the Max Planck Insti­tute for Astron­o­my in Hei­del­berg.

The Milky Way Galaxy is a barred spi­ral galaxy: a disk-shaped col­lec­tion of dust, gas and bil­lions of stars, 100,000 light-years in diam­e­ter. It is far from a sim­ple disk struc­ture, being com­prised of two spi­ral arms, a bar-shaped fea­ture that runs through its cen­tre, and a cen­tral bulge of stars. The cen­tral bulge, like oth­er barred galaxy’s bulges, resem­bles a rec­tan­gu­lar box or peanut when viewed—as we view it—from with­in the plane of the galaxy. The X‑shaped struc­ture is an inte­gral com­po­nent of the bulge.

Astronomers think the bulge could have formed in two dif­fer­ent ways: it may have formed when the Milky Way Galaxy merged with oth­er galax­ies; or it may have formed with­out the help of exter­nal influ­ences as an out­growth of the bar, which itself forms from the evolv­ing galac­tic disk. Lang and Ness’s find­ing sup­ports the lat­ter mod­el which pre­dicts the box- or peanut-shaped bulge and the galac­tic X.

This lat­est, clear­est view of the bulge emerged when Lang re-ana­lyzed pre­vi­ous­ly released data from the Wide-field Infrared Sur­vey Explor­er (WISE), a space tele­scope launched by NASA in 2009. Before end­ing its ini­tial mis­sion in 2011, WISE sur­veyed the entire sky in infrared—imaging three-quar­ters of a bil­lion galax­ies, stars and aster­oids.

“The bulge is a key sig­na­ture of for­ma­tion of the Milky Way Galaxy,” says Ness. “If we under­stand the bulge we will under­stand the key process­es that have formed and shaped our galaxy.”

“The shape of the bulge tells us about how it has formed. We see the X‑shape and boxy mor­phol­o­gy so clear­ly in the WISE image and this demon­strates that inter­nal for­ma­tion process­es have been the ones dri­ving the bulge for­ma­tion.”

It is also evi­dence that our galaxy did not expe­ri­ence major merg­ing events since the bulge formed. If it had, inter­ac­tions with oth­er galax­ies would have dis­rupt­ed its shape.

Lang’s analy­sis was orig­i­nal­ly intend­ed to aid in his research in map­ping the web of galax­ies beyond the Milky Way Galaxy. To help explore the maps he’d devel­oped from the WISE data, he cre­at­ed an inter­ac­tive map-brows­ing web­site and tweet­ed an image of the entire sky.

“Ness saw the tweet and imme­di­ate­ly rec­og­nized the impor­tance of the X‑shaped struc­ture,” says Lang. “We arranged to meet at an upcom­ing con­fer­ence we were both attend­ing. The paper was born from that meet­ing. That’s the pow­er of large sur­veys and open sci­ence!”

Sup­ple­men­tary notes:

1) NASA’s Jet Propul­sion Lab­o­ra­to­ry, Pasade­na, Cal­i­for­nia, man­ages and oper­ates WISE for NASA’s Sci­ence Mis­sion Direc­torate in Wash­ing­ton. The space­craft was put into hiber­na­tion mode in 2011, after it scanned the entire sky twice, there­by com­plet­ing its main objec­tives. In Sep­tem­ber 2013, WISE was reac­ti­vat­ed, renamed NEOWISE and assigned a new mis­sion to assist NASA’s efforts to iden­ti­fy poten­tial­ly haz­ardous near-Earth objects. For more infor­ma­tion on WISE:

2) With con­tri­bu­tions from the Max Planck Insti­tute for Astron­o­my and NASA Jet Propul­sion Lab­o­ra­to­ry.


The X‑shaped Bulge of the Milky Way Revealed by WISE:–6256/152/1/14

Con­tact details:

Dr. Dustin Lang
Research Asso­ciate
Dun­lap Insti­tute for Astron­o­my & Astro­physics
Uni­ver­si­ty of Toron­to
Skype: dst­nd­stn
Google Chat:
Twit­ter: @dstndstn

Chris Sasa­ki
Com­mu­ni­ca­tions Coor­di­na­tor, Pub­lic Infor­ma­tion Offi­cer
Dun­lap Insti­tute for Astron­o­my & Astro­physics
Uni­ver­si­ty of Toron­to
p: 416–978-6613

Dr. Melis­sa Ness
Max Planck Insti­tute for Astron­o­my
Hei­del­berg, Ger­many
Twit­ter: @melissakness

Dr. Markus Poes­sel
Pub­lic Rela­tions
Max Planck Insti­tute for Astron­o­my
Hei­del­berg, Ger­many
p: (+49 | 0) 6221 528–261

Eliz­a­beth Lan­dau
Media Rela­tions Spe­cial­ist
NASA Jet Propul­sion Lab­o­ra­to­ry
Pasade­na, Calif.
p: (818) 354‑6425

The Dun­lap Insti­tute for Astron­o­my & Astro­physics at the Uni­ver­si­ty of Toron­to is an endowed research insti­tute with over 40 fac­ul­ty, post­docs, stu­dents and staff, ded­i­cat­ed to inno­v­a­tive tech­nol­o­gy, ground­break­ing research, world-class train­ing, and pub­lic engage­ment. The research themes of its fac­ul­ty and Dun­lap Fel­lows span the Uni­verse and include: opti­cal, infrared and radio instru­men­ta­tion, Dark Ener­gy, large-scale struc­ture, the Cos­mic Microwave Back­ground, the inter­stel­lar medi­um, galaxy evo­lu­tion, cos­mic mag­net­ism and time-domain sci­ence. The Dun­lap Insti­tute, togeth­er with the Depart­ment of Astron­o­my & Astro­physics, the Cana­di­an Insti­tute for The­o­ret­i­cal Astro­physics, and the Cen­tre for Plan­e­tary Sci­ences, com­prise the lead­ing research cen­tre for astron­o­my in Cana­da, at the lead­ing research uni­ver­si­ty in the coun­try. The Dun­lap Insti­tute is com­mit­ted to mak­ing its sci­ence, train­ing and pub­lic out­reach activ­i­ties pro­duc­tive and enjoy­able for every­one, regard­less of gen­der, sex­u­al ori­en­ta­tion, dis­abil­i­ty, phys­i­cal appear­ance, body size, race, nation­al­i­ty or reli­gion.