Is dark matter made of black holes

first_imgThe merger of unexpectedly large black holes has led to speculation that they could be dark matter. Click to view the privacy policy. Required fields are indicated by an asterisk (*) Is dark matter made of black holes? Sign up for our daily newsletter Get more great content like this delivered right to you! Country 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 Mark Garlick/Science Source center_img By Adrian ChoFeb. 9, 2017 , 9:00 AM Email Could dark matter consist of primordial black holes, as numerous as the stars? It’s an old, improbable idea, but it made a Lazarus-like comeback a year ago, when the discovery of gravitational waves suggested that the cosmos abounds with unexpectedly heavy black holes. With decades-long searches failing to find the hypothetical dark matter particles that theorists have favored, physicists are turning to more radical ways of explaining the universe’s missing mass.“It’s a nutty idea,” says Marc Kamionkowski, a theorist at Johns Hopkins University in Baltimore, Maryland, whose team made the case for black hole dark matter here last week at a meeting of the American Physical Society. “But every idea of what dark matter might be is a nutty idea.” Others are skeptical, and new studies add to the doubts. For the idea to hold up, “I think you need some miracles,” says Daniel Holz, a theorist at the University of Chicago in Illinois.Ordinary black holes form when individual stars collapse, and were thought to top out at about 15 times the mass of the sun. And the supermassive black holes that lurk in galactic centers swallow billions of stars. But astrophysicists didn’t see how collapsing stars could form black holes of intermediate masses. That’s why it was a surprise when physicists with the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced in February 2016 that they had detected ripples in space from the violent merger of two black holes 29 and 36 times as massive as our sun. Theorists say there is a way to form such heavy black holes even before the first stars: through the direct collapse of dense spots in the seething plasma of particles that filled the cosmos right after the big bang. If LIGO’s discovery wasn’t a statistical burp, space could teem with these primordial black holes, says Kamionkowski—enough to account for the 85% of the universe’s matter that is missing.They should also have left a mark on the cosmic microwave background (CMB). X-rays from matter swirling into the black holes should have ionized some of the first atoms, which would have altered the CMB’s mottled appearance. Kamionkowski and colleagues calculate black holes between 20 and 100 solar masses could be consistent with CMB measurements. But Massimo Ricotti, a cosmologist at the University of Maryland in College Park, who did an earlier calculation with different assumptions, thinks “it would be very difficult to have all the dark matter in 30-solar-mass black holes.”Observations of galaxies today cast a different doubt on black hole dark matter, reports Timothy Brandt, an astrophysicist at the Institute for Advanced Study in Princeton, New Jersey. Black holes heavier than 10 solar masses should have long ago settled to the centers of small galaxies, churning up stars with their gravity like bowling balls setting the pins flying. That would have puffed up the galaxies. However, Brandt examined five faint dwarf galaxies near the Milky Way, and found them to be compact and unruffled. “That’s a very strong argument against this sort of dark matter,” he says.Heavy black holes might also betray their presence by occasionally passing in front of more distant stars. Their gravity would magnify the star, causing it to temporarily brighten in an effect called microlensing. Two microlensing surveys in the 1990s ruled out the possibility of swarms of black holes. But because the surveys were short, they were only sensitive to relatively small black holes. Brightening events for 30-solar-mass black holes would stretch out for years, so they haven’t yet been ruled out, says Ely Kovetz, a cosmologist at Johns Hopkins.Kovetz also hopes that confirmation could come from new radio telescopes coming online, such as the Canadian Hydrogen Intensity Mapping Experiment (CHIME) in Okanagan Falls. Since 2007, astronomers have known of millisecond flashes of radio waves called fast radio bursts (FRBs). Microlensing by a 30-solar-mass black hole should generate a rapid echo of a burst, making the black hole easier to detect. CHIME should spot thousands of FRBs in a few years, Kovetz says, enough to look for telltale echoes.Katelin Schutz, a theorist at the University of California, Berkeley, says that clarity could come even faster from stellar beacons called millisecond pulsars, which emit exquisitely regular pulses of radio waves. Microlensing by a black hole should slightly slow the pulses, she reports. Those shifts would occur over years, but radio astronomers already have 30 years of data they can search through, she says.The LIGO discovery sparked this debate, but LIGO is unlikely to end it. Last June, the consortium reported a second black hole merger, but the black holes involved weighed just 8 and 14 solar masses. And last week, LIGO said it had found two “triggers” in new data taken since November 2016—which could also end up being black hole mergers. But Kovetz says LIGO would need to spot about 100 black holes before a true census of their masses emerges. That could take a decade.last_img