|
00;00;01;17 - 00;00;03;23 [Music throughout] 00;00;03;27 - 00;00;06;03 Hi. My name is Judy Racusin. 00;00;06;03 - 00;00;09;27 I'm the deputy project scientist on the Fermi Gamma-ray Space Telescope. 00;00;10;00 - 00;00;14;16 I'm here today to watch a video with you of 14 years of observations 00;00;14;16 - 00;00;18;06 collected by the Fermi Large Area Telescope, or the LAT. 00;00;18;08 - 00;00;20;25 This is the primary instrument on the Fermi mission, 00;00;20;25 - 00;00;24;00 and it surveys the entire sky every few hours. 00;00;24;03 - 00;00;26;19 This allows it to do a lot of really cool things. 00;00;26;19 - 00;00;29;10 It can look at sources that vary on timescales 00;00;29;10 - 00;00;32;08 from a fraction of a second to years on end. 00;00;34;29 - 00;00;37;14 There are two different kinds of maps that we're going to look at. 00;00;37;14 - 00;00;40;08 One map is in galactic coordinates. 00;00;40;08 - 00;00;43;08 That means that there's a thin band across the middle of the image, 00;00;43;08 - 00;00;44;22 and that's the Milky Way. 00;00;44;22 - 00;00;47;15 You've probably seen images of the Milky Way in the optical. 00;00;51;27 - 00;00;53;27 The Milky Way in the gamma rays looks kind of similar, 00;00;53;27 - 00;00;57;29 except we're looking at a number of different types of objects. 00;00;58;02 - 00;01;01;03 We'll also look at the gamma-ray sky from another perspective, 00;01;01;03 - 00;01;04;10 where we're looking up and down out of the galaxy which gives us 00;01;04;10 - 00;01;07;11 a much better view of the extragalactic sky 00;01;07;16 - 00;01;11;20 and all the sources way outside our galaxy in the distant universe. 00;01;11;23 - 00;01;15;13 In this map of the gamma ray sky, where we have blue and red 00;01;15;13 - 00;01;19;29 and yellow tones, what we're seeing are actually intensity maps. 00;01;20;01 - 00;01;23;27 Fermi isn't an imaging instrument like you think of Hubble or Webb. 00;01;23;29 - 00;01;26;17 What it is is it's actually a photon-collecting instrument. 00;01;26;17 - 00;01;28;21 It's a particle detector in space. 00;01;28;21 - 00;01;32;21 And we make these maps by adding up all of the photons we collect. 00;01;32;24 - 00;01;36;16 In this case, these are over four days. 00;01;36;19 - 00;01;38;29 The color scheme, blue, red, yellow. 00;01;38;29 - 00;01;43;07 This is just a way for us to visualize it because our eyes don't see gamma rays. 00;01;43;10 - 00;01;45;29 Those circular sources that you see in the galactic plane 00;01;45;29 - 00;01;47;20 are actually individual objects. 00;01;47;20 - 00;01;49;11 Most of those are pulsars. 00;01;49;11 - 00;01;53;01 These are rapidly spinning, dense, stellar remnants called neutron stars 00;01;53;07 - 00;01;57;20 that are actually varying, pulsing on timescales from hundreds 00;01;57;26 - 00;02;01;13 of times per second to several seconds. 00;02;01;16 - 00;02;03;25 We see sources above and below 00;02;03;25 - 00;02;07;06 the galactic plane. Those are largely blazars. 00;02;07;12 - 00;02;11;24 What that is, is a supermassive black hole, millions to billions of times 00;02;11;24 - 00;02;15;14 the mass of our Sun, the center of a galaxy that is active. 00;02;15;22 - 00;02;19;18 That means that there's gas and stars falling into it, 00;02;19;20 - 00;02;24;18 and it produces jets of emission And they're very chaotic systems. 00;02;24;21 - 00;02;27;08 So they are turning on and they're turning off. 00;02;27;08 - 00;02;29;09 And that's actually the source of a lot of the variability 00;02;29;09 - 00;02;32;18 that we'll see throughout this movie. 00;02;32;21 - 00;02;33;15 We have a team 00;02;33;15 - 00;02;37;05 of dedicated scientists, what we call the flare advocates. 00;02;37;08 - 00;02;39;26 Their job is to look at data every day 00;02;39;26 - 00;02;43;03 that comes from Fermi and look for these flaring sources. 00;02;43;05 - 00;02;45;03 It's not just so that we know that they're there 00;02;45;03 - 00;02;48;09 and that we catalog them, but some sources are interesting enough 00;02;48;09 - 00;02;51;16 that we want to tell our friends – other space and ground-based telescopes – 00;02;51;16 - 00;02;56;11 that they should go look at the same place and collect multiwavelength data 00;02;56;17 - 00;02;59;05 so we can better understand these outbursts. 00;03;03;19 - 00;03;04;18 You might notice 00;03;04;18 - 00;03;07;18 there are a few odd discontinuities in these images. 00;03;07;22 - 00;03;11;03 This is a result of holes in the data that we didn't want to be distracting. 00;03;11;09 - 00;03;15;04 So we patched those images using frames before or after. 00;03;18;07 - 00;03;21;16 If you look carefully, you see one source that isn't like the others. 00;03;21;18 - 00;03;23;02 It's actually moving. 00;03;23;02 - 00;03;25;04 And sometimes it gets brighter or fainter. 00;03;25;04 - 00;03;26;28 That's actually just the Sun. 00;03;26;28 - 00;03;29;02 The Sun is an interesting source in the gamma rays. 00;03;29;02 - 00;03;32;01 It's not the brightest source in the sky like it is in the optical, 00;03;32;04 - 00;03;35;07 but it's prominent in its quiescent state 00;03;35;12 - 00;03;39;03 where we're just seeing cosmic rays interacting with the solar atmosphere. 00;03;39;09 - 00;03;41;26 We also see it when there are solar flares. 00;03;45;28 - 00;03;47;08 That bright flash right there 00;03;47;08 - 00;03;49;17 was a spectacular solar flare. 00;03;58;29 - 00;04;02;23 You may have noticed a lot of variations in the sky over time. 00;04;02;29 - 00;04;06;13 It’s not that the galaxy itself is getting brighter or fainter. 00;04;06;13 - 00;04;11;01 It's that as Fermi surveys the sky, it doesn't do it completely evenly. 00;04;11;03 - 00;04;14;29 Over many years, we accumulate a very nice, even exposure of the sky, 00;04;15;02 - 00;04;18;08 but when we look at short timescales, what we're seeing are variations 00;04;18;08 - 00;04;21;12 in the survey, not actual variations in the sky. 00;04;21;13 - 00;04;25;07 But when you do see individual sources, those are real variations – 00;04;25;13 - 00;04;28;14 from our own solar system out to the distant universe. 00;04;37;12 - 00;04;39;27 The sky exposure pattern seems to change a bit 00;04;39;27 - 00;04;41;26 starting about 2018. 00;04;41;26 - 00;04;46;09 This was due to a hardware issue where one of our solar panels stopped rotating. 00;04;46;13 - 00;04;48;28 It's still fully functional and Fermi has enough power 00;04;48;28 - 00;04;51;28 to operate both instruments and the observatory. 00;04;52;02 - 00;04;52;25 What it means, though, 00;04;52;25 - 00;04;56;29 is that the way we observe the sky and the timescales in which we survey 00;04;57;02 - 00;04;58;07 have changed a bit. 00;05;08;11 - 00;05;13;10 In our 14-year map there's over 7,000 total sources. 00;05;13;13 - 00;05;18;05 Almost 4,000 of those are these active galaxies, these blazars. 00;05;18;07 - 00;05;22;16 There are several hundred pulsars and in total something like 00;05;22;19 - 00;05;25;16 2,000 of these sources are variable. 00;05;33;09 - 00;05;34;03 This video 00;05;34;03 - 00;05;38;11 showing the first 14 years of Fermi observations is just the beginning. 00;05;38;14 - 00;05;41;15 Fermi continues to observe the dynamic sky every day, 00;05;41;15 - 00;05;44;10 and we hope it'll continue to do so for many years into the future. 00;05;57;27 - 00;06;09;11 Cumulative 14-Year Fermi Sky 00;06;09;28 - 00;06;14;29 NASA |