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[Music]

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when a massive star explodes as a

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supernova its core may be crushed into

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one of two types of compact remnant a

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black hole or a neutron star

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neutron stars are the size of a city but

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contain more mass than our sun

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they rotate rapidly host powerful

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magnetic fields and produce beams of

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radiation that emit a wide range of

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energy

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when we detect pulses as the beams sweep

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over earth the object is known as a

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pulsar

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they can spin many times per second on

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their axes the fastest pulsars spin over

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700 times per second

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and that rapidly spinning massive object

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generates extremely strong

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magnetic fields and accelerates

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particles to high energies and we see

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that

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those accelerated particles emitting

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energy in the form of gamma rays x-rays

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and radio waves and when that beam

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sweeps past the line of sight to the

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earth we see it pulse on and that's why

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they're named pulsars

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the most sensitive tool for observing

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pulsars and gamma-ray light is nasa's

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fermi gamma-ray space telescope

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fermi scans the entire sky for

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high-energy sources and has found many

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previously undetected gamma-ray emitters

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scientists have identified many of these

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but for some the source of the gamma

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rays remains unknown

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i got interested a couple years ago in

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trying to find the limits of what fermi

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can discover how extreme these objects

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can be and in order to do that i focused

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on this set of objects that are

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relatively bright and well measured by

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fermi

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and found that virtually all of them

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have now been identified at present when

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i started this project there were only

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six objects which hadn't been we hadn't

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figured out what they were yet despite

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intense searches at radio with radio

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wavelengths which is the standard way in

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which people find pulsars and also

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looking at the gamma rays themselves no

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pulsations had been seen so something

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was unique about these six objects and i

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thought hmm that's where the discovery

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space is going to be if we can track

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down what those are we have a good

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chance of finding something new

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we took this small set of six objects

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and attacked them with a number of wave

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bands but i think the thing that helped

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us make the greatest progress was

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looking in the optical invisible light

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now this may seem a little bit unusual

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for studying the high-energy gamma-ray

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universe but it turns out that many of

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these objects seem to have optical

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counterparts and if you can figure out

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what the visible light counterpart of an

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object is you've a long ways along the

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track to understanding what it's all

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about

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it was roger romani's optical

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observations that discovered a

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counterpart to the gamma-ray source that

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showed a binary period that was

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indicative of this potentially being a

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binary millisecond pulsar it brightened

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and it dimmed and brightened

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and so this looked like we were

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looking at possibly something which was

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irradiated by a companion pulsar

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and that every time you're looking at

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the bright face you see a bright optical

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source and when it rotates away from you

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and you see the dark face you don't see

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anything

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we managed to get enough observations of

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the object to piece together its orbital

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period and found uh remarkably that it

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was an incredibly heated object blue

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white on one side deep deep red on the

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other that was orbiting around something

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invisible with an orbital period about

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one and a half hours

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now

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that's faster than any spin powered

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pulsar ever known and indicates that

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it's a really really tight system and

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that the gamma rays are blasting the

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companion at point-blank range

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our colleagues of germany managed to use

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the orbital period that we'd measured to

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search in the gamma rays directly and

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with a computational tour to force

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managed to find the pulse signal of the

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pulsar directly in the gamma rays

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themselves

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what i'm doing is blind searches for

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pulsars so

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that we try to find pulses that have not

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been seen before

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so you don't know how fast the pulse is

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spinning where exactly it is sitting in

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the sky to do that you have basically to

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try every possible combination of

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parameters if they match your data

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output stream

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so the problem is that the number of

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possible combinations is tremendously

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high so the straightforward brute force

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approach isn't possible the

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computational power you would need would

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be in excess of what's available in the

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whole planet

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so our work is to invent more efficient

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methods to do that

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the basic method is analogous to zooming

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it's similar to changing your

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uh objectives of your microscope in

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favor of one of higher magnification so

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you look at one interesting point on the

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slide and then you zoom in on that and

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then you further zoom in if it still is

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interesting

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to find the pulsations in the gamma-ray

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data

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uh required us about

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5000 cpu

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days so

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so if you do it on your laptop you need

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5000 days

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um but if you have five thousand laptops

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you only one day and so

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that's the path we took because we have

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a computing cluster that's called atlas

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at the albert einstein institute in

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hanover and that computing facility we

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used for this analysis and it was

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immediately clear this is a detection so

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it's not it cannot be a noise

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fluctuation because it's so

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so loud in the data

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a pulsar that was a strong gamma ray

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source yet showed no radio signature

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intrigued researchers

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among them was paul ray of the naval

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research laboratory he and his team

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thought they might have a solution to

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the puzzling lack of radio emission

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when we first discovered the system i

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looked back at our archival radio

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observations and none of them showed

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detections of this pulsar we think that

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nearly all pulsars do emit radio waves

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the radio beam is emitted from most

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pulsars from a region above the polar

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cap of the star and that means it's a

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tightly concentrated flashlight type

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beam

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in a system like this where there's wind

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being blown off the companion star

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there's a lot of obscuring material

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along the line of sight it might be that

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it is a radio pulsar and we just

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couldn't see it and the one way to

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confront that is to use a higher radio

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frequency that's more penetrating that's

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less affected by the scattering in the

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in the intervening material and so we

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went and made an observation with the

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robert c byrd green bank telescope run

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by the national radio astronomy

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observatory in west virginia at a much

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higher frequency than typical radio

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observations and it was in one of those

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observations that we first saw the

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signal from the system and it appears

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that it is most of the time obscured by

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the material from its companion

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a combination of radio optical and gamma

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ray data allowed astronomers to assemble

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a complete picture of the system it

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turned out to be a rare black widow

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binary where a rejuvenated pulsar is

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gradually evaporating a low-mass

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companion star they get this name

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because they are in very close systems

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with the companion star being close

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enough to the neutron star that the

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neutron star is irradiating the

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companion so the neutron stars producing

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a wind of energetic particles and

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magnetic fields and also all the gamma

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rays that are radiated all this hits the

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companion star and heats it up to very

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high temperatures but only on one side

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so the side that's towards the neutron

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star gets blasted by this pulsar wind

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and it has been whittled away over

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billions of years to where it now is

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only about eight times the mass of

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jupiter

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this whole system is about the size of

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the earth moon system so it's very

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compact

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we see the pulsar at the center

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spinning and emitting beams of radio and

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gamma rays the radio waves are

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represented by the green and the gamma

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rays are represented by the magenta

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that radiation that impinges on the star

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is blowing off clouds of ionized

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material that are collecting around the

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system and that's what obscures the

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radio emission so we see that most of

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the time the radio and represented in

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green only makes it to that obscuring

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material and not through it while the

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gamma rays which are much more

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penetrating go right through

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it turns out that in as far as it's a

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pulsar it's not so very unusual what's

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unusual about it is this binary system

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and the binary system seems to have

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through its history allowed this neutron

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star pulsar to accrete enormous amounts

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of mass the measurements to date suggest

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that it's very heavy indeed and heavy

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neutron stars push the absolute extreme

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of the densest matter in our visible

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universe i say this because many people

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think of black holes as being exotic in

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the most extreme objects known but after

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all a black hole is collapsed to the

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point where nothing is visible it's

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black a neutron star is an object that's

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on the hairy edge of becoming a black

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hole yet is still visible in our

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universe

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hence the study of these ultra massive

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neutron stars gives us the opportunity

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to study the most extreme matter in our

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visible universe

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if this fellow is as heavy as he seems

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he pushes that study to a new horizon to