{"id":23579,"date":"2021-09-16T00:00:00","date_gmt":"2021-09-16T00:00:00","guid":{"rendered":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/?post_type=purple_issue&p=23579"},"modified":"2021-10-22T11:47:34","modified_gmt":"2021-10-22T11:47:34","slug":"qa-with-a-gravitational-wave-astronomer","status":"publish","type":"post","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/2021\/09\/16\/qa-with-a-gravitational-wave-astronomer\/","title":{"rendered":"Q&A with a Gravitational Wave Astronomer"},"content":{"rendered":"\n

Shaoni Bhattacharya interviews Professor James Cordes<\/h4>\n\n

Voyager 1\u2019s discovery of a \u2018plasma hum\u2019 outside our Solar System may be critical for finding future gravitational waves<\/p>\n\n

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Voyager 1\u2019s exploration of the interstellar medium is helping scientists to gather data about turbulence and its effect on gravitational wave detection ILLUSTRATION<\/figcaption><\/figure><\/div>\n\n

What is Voyager 1 doing now?<\/strong><\/p>\n\n

It\u2019s over 40 years since the Voyager 1 and 2 spacecraft were launched in the late 1970s. They have now left the sphere of the Sun\u2019s influence \u2013 the heliosphere \u2013 and they are both sampling the conditions in the interstellar medium. This connects up with what I do, using ground-based radio telescopes to also study the interstellar medium.<\/p>\n\n

How did you use mission data from Voyager 1 in your recent study in Nature Astronomy? <\/em><\/strong><\/p>\n\n

We analysed the signal from Voyager 1\u2019s Plasma Wave System (PWS), which uses antennae that hang off the spacecraft and measures low frequency radio waves. We look for oscillations that are at a frequency which characterises the density of the ionised gas (plasma) in the insterstellar medium<\/p>\n\n

What did you find? <\/strong><\/p>\n\n

We learned that the plasma density changes as Voyager 1 moves along, and some of that change is due to turbulence in the interstellar gas. It\u2019s thin gas, less than one particle per cubic centimetre \u2013 but it\u2019s important on an astronomical scale. Other people had used this instrument to see specific events caused by big flares called coronal mass ejections. We were asking: is there a more continuous signal? We came up with a way of pulling that signal out of the noise in the data and that\u2019s how we identified the \u2018hum\u2019.<\/p>\n\n

What do you think is happening in the interstellar medium to cause this mysterious \u2018hum\u2019?<\/strong><\/p>\n\n

It is electromagnetic waves coming from the oscillation of the plasma, in particular ionised hydrogen \u2013 protons and electrons unbound from each other. The electrons are oscillating back and forth past the heavier protons. The question is, what excites this? With the big events we\u2019ve previously seen, the trigger is a coronal mass ejection. For this signal, though, the cause is not really understood. It could be some residual effects from coronal mass ejections, or it might just be a property of having hot gas that\u2019s moving, or it might be extremely energetic particles from cosmic rays. Whatever the mechanism, it\u2019s not a single event \u2013 it\u2019s something fairly persistent.<\/span><\/p>\n\n

Could we listen to the \u2018plasma hum\u2019?<\/strong><\/p>\n\n

No, it\u2019s not really sound, it\u2019s a radio signal that\u2019s been measured. However, it\u2019s at the same frequency that we can hear, so you can translate the electromagnetic signal into sound the way a radio does.<\/p>\n\n

What are the implications of your findings?<\/strong><\/p>\n\n

There are several implications. One is on the role of turbulence in the interstellar gas. New stars are forming out of gas clouds and there\u2019s turbulence there as well. So there are these deep physical connections between the very thin gas and dense gas that ultimately forms planets and stars.<\/p>\n\n

Why does interstellar turbulence matter? <\/strong><\/p>\n\n

The other is cosmic rays: they are energetic particles, so how do they get that energy? The understanding is that shock fronts accelerate those particles; but they don\u2019t move in a straight line, they make a random \u2018drunkard\u2019s walk\u2019 because of turbulence in the interstellar medium. Voyager 1 may tell us about what that looks like on a smaller scale. The last connection is more astronomical. We know about twinkling stars, their light varies due to turbulence in Earth\u2019s atmosphere. We see a similar effect on radio waves viewed through interstellar turbulence; it can limit our precision in measurements.<\/p>\n\n

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James Cordes is the George Feldstein Professor of Astronomy at Cornell University and a co-principal investigator of NANOGrav (the North American Nanohertz Observatory for Gravitational Waves). <\/p>\n<\/div>\n<\/div>\n\n

PHOTO: NASA\/JPL-CALTECH<\/p>\n","protected":false},"excerpt":{"rendered":"

Shaoni Bhattacharya interviews Professor James Cordes<\/p>\n","protected":false},"author":24,"featured_media":23577,"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":"October-2021","purple_custom_meta_purple_source_issue":"October-2021","purple_external_id":"October-2021-98-1","purple_custom_meta_purple_external_id":"October-2021-98-1","purple_issue_code":"|0000086545||","purple_custom_meta_purple_issue_code":"|0000086545||","purple_android_product":"com.im.skyatnight.197","purple_custom_meta_purple_android_product":"com.im.skyatnight.197","purple_ios_product":"com.im.skyatnight.197","purple_custom_meta_purple_ios_product":"com.im.skyatnight.197","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\/2021\/09\/38bef400-9886-491e-938d-90e39bef489a.jpg","author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/author\/importmanagerhubsprylab-com\/"},"acf":{"readingTimeMinutes":"4"},"uagb_featured_image_src":{"full":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/09\/38bef400-9886-491e-938d-90e39bef489a.jpg",983,706,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/09\/38bef400-9886-491e-938d-90e39bef489a-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/09\/38bef400-9886-491e-938d-90e39bef489a-300x215.jpg",300,215,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/09\/38bef400-9886-491e-938d-90e39bef489a-768x552.jpg",768,552,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/09\/38bef400-9886-491e-938d-90e39bef489a.jpg",800,575,false],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/09\/38bef400-9886-491e-938d-90e39bef489a.jpg",983,706,false],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/09\/38bef400-9886-491e-938d-90e39bef489a.jpg",983,706,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":"Shaoni Bhattacharya interviews Professor James Cordes","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts\/23579"}],"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=23579"}],"version-history":[{"count":17,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts\/23579\/revisions"}],"predecessor-version":[{"id":24940,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts\/23579\/revisions\/24940"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media\/23577"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media?parent=23579"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/categories?post=23579"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/tags?post=23579"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}