Large strangely dim galaxy found lurking on far side of Milky Way

first_img By Adam MannNov. 13, 2018 , 12:30 PM Sign up for our daily newsletter Get more great content like this delivered right to you! Country G. Torrealba, Academia Sinica, Taiwan; V. Belokurov, Cambridge, U.K. and CCA, New York, U.S., based on an image by ESO/S. Brunie Country * Afghanistan Aland Islands Albania Algeria Andorra Angola Anguilla Antarctica Antigua and Barbuda Argentina Armenia Aruba Australia Austria Azerbaijan Bahamas Bahrain Bangladesh Barbados Belarus Belgium Belize Benin Bermuda Bhutan Bolivia, Plurinational State of Bonaire, Sint Eustatius and Saba Bosnia and Herzegovina Botswana Bouvet Island Brazil British Indian Ocean Territory Brunei Darussalam Bulgaria Burkina Faso Burundi Cambodia Cameroon Canada Cape Verde Cayman Islands Central African Republic Chad Chile China Christmas Island Cocos (Keeling) Islands Colombia Comoros Congo Congo, the Democratic Republic of the Cook Islands Costa Rica Cote d’Ivoire Croatia Cuba Curaçao Cyprus Czech Republic Denmark Djibouti Dominica Dominican Republic Ecuador Egypt El Salvador Equatorial Guinea Eritrea Estonia Ethiopia Falkland Islands (Malvinas) Faroe Islands Fiji Finland France French Guiana French Polynesia French Southern Territories Gabon Gambia Georgia Germany Ghana Gibraltar Greece Greenland Grenada Guadeloupe Guatemala Guernsey Guinea Guinea-Bissau Guyana Haiti Heard Island and McDonald Islands Holy See (Vatican City State) Honduras Hungary Iceland India Indonesia Iran, Islamic Republic of Iraq Ireland Isle of Man Israel Italy Jamaica Japan Jersey Jordan Kazakhstan Kenya Kiribati Korea, Democratic People’s Republic of Korea, Republic of Kuwait Kyrgyzstan Lao People’s Democratic Republic Latvia Lebanon Lesotho Liberia Libyan Arab Jamahiriya Liechtenstein Lithuania Luxembourg Macao Macedonia, the former Yugoslav Republic of Madagascar Malawi Malaysia Maldives Mali Malta Martinique Mauritania Mauritius Mayotte Mexico Moldova, Republic of Monaco Mongolia Montenegro Montserrat Morocco Mozambique Myanmar Namibia Nauru Nepal Netherlands New Caledonia New Zealand Nicaragua Niger Nigeria Niue Norfolk Island Norway Oman Pakistan Palestine Panama Papua New Guinea Paraguay Peru Philippines Pitcairn Poland Portugal Qatar Reunion Romania Russian Federation Rwanda Saint Barthélemy Saint Helena, Ascension and Tristan da Cunha Saint Kitts and Nevis Saint Lucia Saint Martin (French part) Saint Pierre and Miquelon Saint Vincent and the Grenadines Samoa San Marino Sao Tome and Principe Saudi Arabia Senegal Serbia Seychelles Sierra Leone Singapore Sint Maarten (Dutch part) Slovakia Slovenia Solomon Islands Somalia South Africa South Georgia and the South Sandwich Islands South Sudan Spain Sri Lanka Sudan Suriname Svalbard and Jan Mayen Swaziland Sweden Switzerland Syrian Arab Republic Taiwan Tajikistan Tanzania, United Republic of Thailand Timor-Leste Togo Tokelau Tonga Trinidad and Tobago Tunisia Turkey Turkmenistan Turks and Caicos Islands Tuvalu Uganda Ukraine United Arab Emirates United Kingdom United States Uruguay Uzbekistan Vanuatu Venezuela, Bolivarian Republic of Vietnam Virgin Islands, British Wallis and Futuna Western Sahara Yemen Zambia Zimbabwe Antlia 2 (upper left), hidden on the Milky Way’s far side, is as big as the Large Magellanic Cloud (lower right) but much dimmer. (A bright, artificial blob representing Antlia 2 was added to show its location.) Large, strangely dim galaxy found lurking on far side of Milky Waycenter_img Circling our galaxy is a stealthy giant. Astronomers have discovered a dwarf galaxy, called Antlia 2, that is one-third the size of the Milky Way itself. As big as the Large Magellanic Cloud, the galaxy’s largest companion, Antlia 2 eluded detection until now because it is 10,000 times fainter. Such a strange beast challenges models of galaxy formation and dark matter, the unseen stuff that helps pull galaxies together.“It’s a very odd object and kind of exciting because we don’t know yet how to interpret all of its properties,” says Andrey Kravtsov of The University of Chicago in Illinois, who was not involved in the work.The galaxy was discovered with data from the European Space Agency’s Gaia satellite, a space telescope measuring the motions and properties of more than 1 billion stars in and around the Milky Way. Gabriel Torrealba, an astronomy postdoc at the Academia Sinica in Taipei, decided to sift the data for RR Lyrae stars. These old stars, often found in dwarf galaxies, shine with a throbbing blue light that pulses at a rate signaling their inherent brightness, allowing researchers to pin down their distance. Email “RR Lyrae are so rare at these distances that even if you see two, you question why they are together,” says Vasily Belokurov, an astronomer at the University of Cambridge in the United Kingdom and a collaborator on the discovery. When the team found three, some 420,000 light-years away, it was “an overwhelming signal” of a large cluster of stars in that location, Belokurov says. But because the RR Lyrae stars lie on the far side of the disk of the Milky Way and its obstructing veil of stars and gas, finding their companions was not easy.Gaia data helped the team see past the foreground stars. Objects in the Milky Way’s disk are close enough for Gaia to measure their parallax: a shift in their apparent position as Earth moves around the sun. More distant stars appear fixed in one spot. After removing the parallax-bearing stars, the researchers homed in on more than 100 red giant stars moving together in the constellation Antlia, they report in a paper posted to the preprint server arXiv this week. The giants mark out a sprawling companion galaxy 100 times less massive than anything of similar size, with far fewer stars.To explain such a diffuse galaxy, Belokurov suggests that early in Antlia 2’s history, many young stars exploded as violent supernovae. This would have blown gas and dust out of the galaxy, weakening its gravity so that it puffed up. An abundance of the heavy elements that are strewn from the guts of exploding stars adds credibility to this idea, says Shea Garrison-Kimmel, an astrophysicist at the California Institute of Technology in Pasadena. Antlia 2 could also have lost matter as stars were tugged away by gravitational tidal forces as it orbited around the larger Milky Way.Even so, its disproportionate size is hard to explain. Galaxies are thought to have formed when the gravity of enormous clumps of dark matter drew in enough ordinary matter to fuel the birth of stars. The team speculates that Antlia 2 might have been born from a fluffier, faster-moving type of dark matter than current models hypothesize.To Garrison-Kimmel, one example isn’t enough to say the dark matter in Antlia 2 is different from that in the Milky Way and its other satellites. “There’s nothing in this one galaxy that screams to me that we need to rethink dark matter,” he says. “But if there are a lot of these, then we might need to take a step back and ask what’s going on.”That could happen now that astronomers know how to find these big, elusive companions. “I think this object is a harbinger,” Kravtsov says. “A taste of things to come.” Click to view the privacy policy. Required fields are indicated by an asterisk (*)last_img

Previous Article
Next Article

Leave a Reply

Your email address will not be published. Required fields are marked *