{"id":44014,"date":"2023-04-18T14:13:18","date_gmt":"2023-04-18T14:13:18","guid":{"rendered":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/?post_type=purple_issue&p=44014"},"modified":"2023-04-27T14:57:07","modified_gmt":"2023-04-27T14:57:07","slug":"qa-with-a-dark-matter-detective","status":"publish","type":"post","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/2023\/04\/18\/qa-with-a-dark-matter-detective\/","title":{"rendered":"Q&A with a dark matter detective"},"content":{"rendered":"\n
Anita Chandran interviews Pavel Mancera Pi\u00f1a<\/h6>\n\n

Q&A with a dark matter detective<\/h2>\n\n

If dark matter accounts for a huge amount of the matter in our Universe, why do some galaxies appear to contain almost none of it? <\/p>\n\n

\"\"
Thinly spread and ghostly dim, ultra-diffuse galaxies buck the trend by holding little or no dark matter <\/figcaption><\/figure><\/div>\n\n

What is dark matter and why is it called \u2018dark\u2019? <\/strong><\/h4>\n\n

We have evidence suggesting that there should be a certain amount of mass in the Universe, but this mass cannot be observed directly. Even in early works from the 1920s, astronomers knew that in order to explain how fast some galaxies move there needed to be more mass than we could account for. An astronomer called Fritz Zwicky came up with the name \u2018dark matter\u2019, but essentially the name only reflects that we don\u2019t really know what it is. <\/p>\n\n

What do we think dark matter might be made of? <\/strong><\/h4>\n\n

Most of the community \u2013 not all \u2013 believes that dark matter is made of particles that don\u2019t interact with electromagnetic radiation, instead only interacting with normal matter through gravity. Essentially, it doesn\u2019t absorb or emit light (and heat). We can only infer that it\u2019s there due to gravitational effects. The problem is that although we have built experiments like the Large Hadron Collider, we haven\u2019t been able to detect dark matter particles, so we don\u2019t know what their exact properties are. <\/p>\n\n

How do you look for dark matter? <\/strong><\/h4>\n\n

By looking at how fast galaxies rotate. We know the rotation of a galaxy is a consequence of its total mass, so if we can observe how fast a galaxy rotates, then we know its total mass. We can compare the total mass measured from how fast the galaxy rotates with the mass of stars and gas [in the galaxy], which we can observe directly from telescopes. We can then look at the mismatch between the two to infer how much dark matter there is in the galaxy. There is typically a very strong mismatch, suggesting that there is a lot of mass that we don\u2019t see. <\/p>\n\n

And what do your investigations show?<\/strong><\/h4>\n\n

Our team was looking at a galaxy that was very peculiar because it\u2019s classified as an \u2018ultra-diffuse\u2019 galaxy. These galaxies are a bit weird because the distribution of light within them is similar to big spiral galaxies like Andromeda or the Milky Way. But they have about 1,000 times less stellar mass than big galaxies. Some people say they have the mass of dwarf galaxies, but the size of giants. We observed the motion of gas in one of these galaxies using the Very Large Array, a set of antennae in New Mexico, to obtain very sharp images. We measured how fast the gas is rotating in this galaxy. And then we tried to see how much dark matter there was. <\/span><\/p>\n\n

Usually, when you look at small galaxies, you find that most of the mass is dark matter. Perhaps 90 per cent, maybe 80 per cent. We found instead that there was a very small contribution from dark matter in this galaxy. In fact, if you take the numbers, you could argue that you don\u2019t need dark matter to explain how fast the galaxy is rotating.<\/span><\/p>\n\n

Why do these ultra-diffuse galaxies have so little dark matter?<\/strong><\/h4>\n\n

According to our understanding of galaxy formation and evolution, all galaxies should have dark matter. So if you see a galaxy with little dark matter it\u2019s very puzzling, though there are some mechanisms that could explain it. We think a potential explanation is that the galaxies have dark matter but that its density is very low. This tells us that the distribution of dark matter in these galaxies \u2013 if there is dark matter \u2013 should be very atypical and completely different to what we expect from our models of galaxy formation and evolution. <\/p>\n\n

What are the implications of galaxies with little to no dark matter?<\/strong><\/h4>\n\n

They challenge the norm in different aspects. Perhaps they are telling us that the distribution of dark matter in galaxies is much broader than what we would have expected. Or perhaps they are telling us that there are other mechanisms that can produce low dark matter densities. I think what is very exciting is that we can use these observations to infer the dark matter content, and perhaps these galaxies can tell us something about the nature of dark matter itself. <\/p>\n\n

<\/p>\n\n

\n\n
\"\"<\/figure><\/div>\n\n

Pavel Mancera Pi\u00f1a is a postdoctoral researcher at Leiden Observatory in the Netherlands, specialising in dark matter<\/p>\n\n

<\/p>\n\n

<\/p>\n\n

<\/div>\n\n

NASA\/ESA AND P. VAN DOKKUM (YALE UNIVERSITY) <\/p>\n","protected":false},"excerpt":{"rendered":"

An interview with Pavel Mancera Pi\u00f1a <\/p>\n","protected":false},"author":24,"featured_media":44012,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"ub_ctt_via":"","purple_page_number":"98","purple_custom_meta_purple_page_number":"98","purple_seq_number":"1","purple_custom_meta_purple_seq_number":"1","purple_source_article":"article_98-1.xml","purple_custom_meta_purple_source_article":"article_98-1.xml","purple_source_issue":"May-2023","purple_custom_meta_purple_source_issue":"May-2023","purple_external_id":"May-2023-98-1","purple_custom_meta_purple_external_id":"May-2023-98-1","purple_issue_code":"|0000086564||","purple_custom_meta_purple_issue_code":"|0000086564||","purple_android_product":"com.im.skyatnight.216","purple_custom_meta_purple_android_product":"com.im.skyatnight.216","purple_ios_product":"com.im.skyatnight.216","purple_custom_meta_purple_ios_product":"com.im.skyatnight.216","purple_web_product":"","purple_custom_meta_purple_web_product":"","purple_publication_id":"075fab74-0a21-4201-866a-899d6c41c40c","purple_migrated":"","kt_blocks_editor_width":""},"categories":[36],"tags":[14],"featured_image_src":"https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/04\/837939dd-d851-4802-96e7-528ddf06a7bb.jpg","author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/author\/importmanagerhubsprylab-com\/"},"acf":{"readingTimeMinutes":"4","apple_news_title":""},"uagb_featured_image_src":{"full":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/04\/837939dd-d851-4802-96e7-528ddf06a7bb.jpg",1040,861,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/04\/837939dd-d851-4802-96e7-528ddf06a7bb-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/04\/837939dd-d851-4802-96e7-528ddf06a7bb-300x248.jpg",300,248,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/04\/837939dd-d851-4802-96e7-528ddf06a7bb-768x636.jpg",768,636,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/04\/837939dd-d851-4802-96e7-528ddf06a7bb-1024x848.jpg",800,663,true],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/04\/837939dd-d851-4802-96e7-528ddf06a7bb.jpg",1040,861,false],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/04\/837939dd-d851-4802-96e7-528ddf06a7bb.jpg",1040,861,false]},"uagb_author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/author\/importmanagerhubsprylab-com\/"},"uagb_comment_info":0,"uagb_excerpt":"An interview with Pavel Mancera Pi\u00f1a","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts\/44014"}],"collection":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/users\/24"}],"replies":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/comments?post=44014"}],"version-history":[{"count":4,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts\/44014\/revisions"}],"predecessor-version":[{"id":44367,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts\/44014\/revisions\/44367"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media\/44012"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media?parent=44014"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/categories?post=44014"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/tags?post=44014"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}