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Why did not we find gravitational waves in our own galaxy?




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For the real black holes that exist or arise in our universe, we can observe the radiation emitted by their surrounding matter and the gravitational waves that exist generated by the inspiration, fusion, and ringdown, but we still need to detect a fusion within our own Milky Way.

LIGO / Caltech / MIT / Sonoma State (Aurore Simonnet)

One of the most spectacular advances in the entire science we were Being able to detect gravitational waves directly: With the unprecedented power and sensitivity of the gravitational wave observatories of LIGO and Virgo, these powerful waves no longer remain undiscovered in space-time, but for the first time you can not only observe them, but also locate the sources they create and learn about their characteristics, and eleven different sources have been discovered so far.

But they are all so far away! Why? is this? this is the quition of Amitava Datta and Chayan Chatterjee who ask:

Why are all known gravitational wave sources (merging binaries) in the distant universe? Why was nobody discovered in our neighborhood? […] My guess (which is most likely wrong) is that the detectors must be exactly aligned for each detection. Therefore, all previous investigations are random.

Find out.

Aerial view of the Virgo gravitational wave detector in Cascina near Pisa (Italy). Virgo is a gigantic Michelson laser interferometer with 3 km long arms and complements the two 4 km long LIGO detectors. These detectors are sensitive to minute changes in distance, which depend on the amplitude of the gravitational wave and not on the energy.

Nicola Baldocchi / Virgo Collaboration

Observatories such as LIGO and Virgo work so that they have two long, vertical arms that hold the most perfect vacuum in the world. Laser light of the same frequency is refracted to traverse these two independent paths, reflected back and forth several times and then rejoined at the end.

Light is just an electromagnetic wave, and when you combine several waves they create an interference pattern. If the interference is constructive, you will see a kind of pattern. If it's destructive, you'll see another guy. Normally, when LIGO and Virgo hang around without gravitational waves, you will see a relatively stable pattern, producing only the random noise (mostly generated by Earth itself) of the instruments.

If the two arms are exactly the same length and do not pass through a gravitational wave, the signal is zero and the interference pattern is constant. As the arm lengths change, the signal is real and oscillating, and the interference pattern changes in a predictable manner over time.

NASA's Space Place

But if you changed the length of one of these arms relative to the armrest arm On the other hand, the time the light travels down the arm also changes. Since light is a wave, a small change in the time the light moves is at another point in the crown's peak / trough pattern, and therefore the interference pattern that results from combining with another light wave changes , [19659004] A single arm could change for a variety of reasons: seismic noise, a jackhammer across the street, or even a truck passing for miles. But there is also an astrophysical source that could cause this change: a passing gravitational wave.

When a gravitational wave crosses a place in space, it causes expansion and compression at alternating times in alternating directions, thereby changing laser arm lengths arising in mutually perpendicular orientations. To take advantage of this physical change, we have developed successful gravitational wave detectors such as LIGO and Virgo.

ESA-C.Carreau

There are two keys that allow us to determine what a gravitational wave is by purely terrestrial noise. [19659018Whengravellingwavesbothesetheretectorbothexhibitchangingthemachinefromthemanyinternalpatternfromindividualimportantimportantimportantimportantimportantimportantfromperiodicpatternoflengthswhichmayleavailablyimposingthatthisignalisavailableforaviationvibrationitisprobablyagravitationalwavethatisonlyagroundbasedsourceofnoise

  • We construct several detectors at different points on the earth. While everyone experiences their own noise due to their local environment, a passing gravitational wave has very similar effects on each of the detectors, separated by milliseconds at most.
  • As you can already see from the first robust evidence of these waves, dating back to observations made on September 14, 2015, both effects are present.

    The inspiration and fusion of the first pair of black holes ever directly observed. The overall signal, along with the noise (above), coincide clearly with the gravitational wave pattern when black holes of a particular mass (center) are joined together and inspired. Notice how frequency and amplitude change at the very end of the fusion.

    B. P. Abbott et al. (LIGO Scientific Collaboration and Virgo Collaboration)

    If we come to the front today, we've actually discovered a large number of mergers: 11 different mergers. Events seem random, because it's only the final stages of inspiration and fusion – the last few seconds or even milliseconds before two black holes or neutron stars collide – that have the right properties to capture even our most sensitive detectors [19659004] However, if we look at the distances to these objects, we find something that could bother us a bit. Although our gravitational wave detectors are the more sensitive to objects the closer they are to us, most of the objects we have found are many hundreds of millions or even billions of light-years away.

    The 11 gravitational wave events discovered by LIGO and Virgo with their names, mass parameters and other key information encoded in tabular form. Note how many events occurred in the last month of the second run: when LIGO and Virgo were running at the same time. The parameter dL is the brightness distance; The closest object is the 2017 neutron star-neutron star cluster, which is ~ 130 million light-years distant.

    LIGO Scientific Collaboration, Virgo Collaboration; arXiv: 1811.12907

    Why is that? If gravitational wave detectors are more sensitive to closer objects, should not we discover them more often, even though we actually observed them?

    There are many possible explanations that might or might not expect this disproportion between what you have to expect. As our questioners have suggested, is it perhaps the orientation? After all, there are many phenomena in this universe, such as pulsars or blazars, that only appear visible when the correct electromagnetic signal is "blasted" directly into our line of sight.

    impression of an artist of an active galactic core. The supermassive black hole in the center of the accretion disk sends a narrow, high-energy matter beam perpendicular to the disk into space. A blazar some 4 billion light years away is the source of many of the highest energy cosmic rays and neutrinos. Only matter from outside the black hole can leave the black hole. Matter from the event horizon can ever escape.

    DESY, Science Communication Lab

    This is a clever idea, but it lacks a fundamental difference between the gravitational forces and the electromagnetic forces. In electromagnetism, electromagnetic radiation is generated by the acceleration of charged particles; In general relativity, gravitational radiation (or gravitational waves) is generated by the acceleration of massive particles. So far so good.

    But in electromagnetism there are both electrical and magnetic fields, and electrically charged particles generate magnetic fields. In this way, you can create and accelerate particles and radiation in a collimated manner. it does not have to be spherical. In gravitation, however, there are only gravitational sources (masses and energetic quanta) and the resulting curvature of space-time.

    If you have two gravitational sources (ie, masses) that inspire and eventually fuse, this motion causes the emission of gravitational waves. A gravitational wave detector, while not intuitive, is sensitive to these waves as a function of 1 / r and not 1 / r ^ 2 and can see these waves in all directions, regardless of whether they are in the face. on or edge-on or somewhere in between.

    NASA, ESA, and A. Feild (STScI)

    As it turns out, it does not really matter if we see an inspiring and merging source of gravitational waves -on, edge, or angle; They still emit gravitational waves with a measurable and observable frequency and amplitude. There may be slight differences in the strength and other characteristics of the signal that depends on orientation in our eyes, but gravitational waves are spherically propagated from a source that generates them, and can be seen from anywhere in the universe for so long. Your detector is sensitive enough ,

    Why are no gravitational waves from binary sources discovered in our own galaxy?

    It may surprise you to discover that there are binary mass sources. like black holes and neutron stars that are now orbiting and inspiring.

    From the very first binary neutron star system ever discovered, we knew that gravitational radiation carried energy away. It was only a matter of time before we found a system in the final stages of inspiration and fusion.

    NASA (L), Max Planck Institute for Radio Astronomy / Michael Kramer

    Long before gravitational waves were discovered directly, we saw what we considered to be an extremely rare configuration: two pulsars orbiting each other. We observed how their pulse time varied in a way that showed their orbital decay due to gravitational radiation. Since then, many pulsars have been observed, including several binary pulsars. In either case, in which we could measure it accurately enough, we see the orbital decay, which shows that they emit gravitational waves.

    Similarly, we have observed X-ray emissions from systems that suggest that this is the case of a black hole in the middle. We've also found that although they're not talked about so often, they are binary X-ray systems in which two black holes orbit each other and emit X-rays that show the masses of both components.

    LIGO and Virgo have discovered a new population of black holes larger in mass than those previously observed on X-ray alone (violet). This graph shows the masses of all ten safe binary black hole fusions detected by LIGO / Virgo (blue) along with the neutron star neutron star fusion (orange). LIGO / Virgo should see several mergers per week with the sensitivity upgrade this week.

    LIGO / Virginia / Northwestern Univ./Frank Elavsky

    These systems are:

    • Rich in Milky Way,
    • Inspire and radiate gravitational waves to save energy,

    • which means using gravitational waves certain frequencies and amplitudes through our detectors,
    • with the sources producing these signals, which one day merge and complete their fusion. 19659049] But we have not observed them in our ground-based gravitational wave detectors. There is a simple, uncomplicated reason for this: Our detectors are in the wrong frequency range!

      The sensitivities of a variety of gravitational wave detectors, old, new and proposed. Pay special attention to Advanced LIGO (in orange), LISA (in dark blue) and BBO (in light blue). LIGO can only detect events with low mass and short period. Low noise, low noise observatories are required for either more massive black holes or for systems that are at an earlier stage of gravitational inspiration.

      Minglei Tong, Class.Quant.Grav. 29 (2012) 155006

      It is only in the final seconds of coalescence that gravitational waves from fused binary files fall into the LIGO / Virgo sensitivity range. In all those millions or even billions of years, when neutron stars or black holes orbit each other and see their orbits decrease, they do so at larger radial distances, which means they take longer to circle each other, which means lower frequency gravitational waves. 19659004] The reason why we do not see any binaries in our galaxy today is that the arms of LIGO and Virgo are too short! If they were millions of miles long, with many reflections, we would have seen them. As it stands now, this will be a significant advance from LISA: it can show us these binary files to be merged in the future, and even predict where and when it will happen!

      The three LISA space probes will be arranged in orbits forming a triangular formation with a center of 20 degrees behind the earth and a side length of 5 million km. This figure is not to scale. LISA is sensitive to much lower frequency sources than LIGO, including future mergers that LIGO will one day see.

      NASA

      True, during the period in which LIGO and Virgo were operating, we have not seen mergers of black holes or neutron stars seen in our own galaxy. That's no surprise. The results of our gravitational wave observations have taught us that there are around 800,000 black-hole binaries in the universe every year. But there are two trillion galaxies in the universe, which means that we have to watch millions of galaxies to get just one event!

      For this reason, our gravitational-wave observatories must be sensitive to distances billions of light-years go in all directions; Otherwise, there just are not enough statistics.

      The range of Advanced LIGO and its ability to spot fused black holes. Although the amplitude of the waves decreases by 1 / r, the number of galaxies increases with the volume: [3].

      LIGO Collaboration / Amber Stuver / Richard Powell / Atlas of the Universe

      There are many neutron stars and black holes that orbit around the universe, including our own Milky Way galaxy. If we look for these systems, either with radio pulses (for the neutron stars) or X-rays (for the black holes), we find them in large quantities. We can even see the evidence for the gravitational waves they emit, though the evidence is indirect.

      If we had more sensitive low-frequency gravitational-wave observatories, we might be able to directly detect the waves produced by sources in our own galaxy. However, if we want to get a true fusion event, they are rare. There may be eons, but the actual events themselves only last a fraction of a second. Only if we throw a very wide net, we can see them at all. Incredibly, the technology for it already exists.


      Submit your Ask Ethan questions to gmail dot com!

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      For the real black holes that exist or can be created in our universe observe the radiation emitted by their surrounding matter and the gravitational waves generated by the inspiration, the merging and the ringdown, but we There is still to be a fusion within our own Milky Way.

      LIGO / Caltech / MIT / Sonoma State

      One of the most spectacular advances in the entire science has been the direct detection of gravitational waves: With the unprecedented power and sensitivity of LIGO and Virgo gravitational wave observatories hold these mighty waves in their hands The fabric of spacetime no longer passes undetected, but for the first time not only can be observed, but also the position of the sources that produce it and their properties parallel sources have been discovered .

      But they are all ready away! Why that? This is the question of Amitava Datta and Chayan Chatterjee who ask:

      Why are all known gravitational wave sources (merging binaries) in the distant universe? Why was nobody discovered in our neighborhood? […] My guess (which is most likely wrong) is that the detectors must be exactly aligned for each detection. Therefore, all previous investigations are random.

      Find out.

      Aerial view of the Virgo gravitational wave detector in Cascina near Pisa (Italy). Virgo is a gigantic Michelson laser interferometer with 3 km long arms and complements the two 4 km long LIGO detectors. These detectors are sensitive to minute changes in distance that are a function of the amplitude of the gravitational wave and not the energy.

      Nicola Baldocchi / Virgo Collaboration

      Observatories like LIGO and Virgo work with two long, vertical arms that have the most perfect vacuum in the world. Laser light of the same frequency is refracted to traverse these two independent paths, reflected back and forth several times and then rejoined at the end.

      Light is just an electromagnetic wave, and when you combine several waves they create an interference pattern. If the interference is constructive, you will see a kind of pattern. If it's destructive, you'll see another guy. Normally, when LIGO and Virgo hang around without gravitational waves, you will see a relatively stable pattern, producing only the random noise (mostly generated by Earth itself) of the instruments.

      If the two arms are exactly the same length and do not pass through a gravitational wave, the signal is zero and the interference pattern is constant. As the arm lengths change, the signal is real and oscillating, and the interference pattern changes in a predictable manner over time.

      NASA's Space Place

      But if you changed the length of one of these arms relative to the armrest arm On the other hand, the time the light travels down the arm also changes. Since light is a wave, a small change in the time the light moves is at another point in the crown's peak / trough pattern, and therefore the interference pattern that results from combining with another light wave changes , [19659004] A single arm could change for a variety of reasons: seismic noise, a jackhammer across the street, or even a kilometer-long passing truck. But there is also an astrophysical source that could cause this change: a passing gravitational wave.

      When a gravitational wave crosses a place in space, it causes expansion and compression at alternating times in alternating directions, thereby changing laser arm lengths arising in mutually perpendicular orientations. To take advantage of this physical change, we have developed successful gravitational wave detectors such as LIGO and Virgo.

      ESA-C.Carreau

      There are two keys that allow us to determine what a gravitational wave is by purely terrestrial noise. [19659018Whengravellingwavesbothesetheretectorbothexhibitchangingthemachinefromthemanyinternalpatternfromindividualimportantimportantimportantimportantimportantimportantfromperiodicpatternoflengthswhichmayleavailablyimposingthatthisignalisavailableforaviationvibrationitisprobablyagravitationalwavethatisonlyagroundbasedsourceofnoise

    • We construct several detectors at different points on the earth. While everyone experiences their own noise due to their local environment, a passing gravitational wave has very similar effects on each of the detectors, separated by milliseconds at most.
    • As you can already see from the first robust evidence of these waves, dating back to observations made on September 14, 2015, both effects are present.

      The inspiration and fusion of the first pair of black holes ever directly observed. The overall signal, along with the noise (above), coincide clearly with the gravitational wave pattern when black holes of a particular mass (center) are joined together and inspired. Notice how frequency and amplitude change at the very end of the fusion.

      B. P. Abbott et al. (LIGO Scientific Collaboration and Virgo Collaboration)

      If we come to the front today, we've actually discovered a large number of mergers: 11 different mergers. Events seem random, because it's only the final stages of inspiration and fusion – the last few seconds or even milliseconds before two black holes or neutron stars collide – that have the right properties to capture even our most sensitive detectors [19659004] However, if we look at the distances to these objects, we find something that could bother us a bit. Although our gravitational wave detectors are more sensitive to objects the closer they are to us, most of the objects we have found are many hundreds of millions or even billions of light-years away.

      The 11 gravitational wave events discovered by LIGO and Virgo with their names, mass parameters and other essential information encoded in tabular form. Note how many events occurred in the last month of the second run: when LIGO and Virgo were running at the same time. The parameter dL is the brightness distance; The closest object is the 2017 neutron star-neutron star cluster, which is ~ 130 million light-years distant.

      LIGO Scientific Collaboration, Virgo Collaboration; arXiv: 1811.12907

      Why is that? If gravitational wave detectors are more sensitive to closer objects, should not we discover them more often, even though we actually observed them?

      There are many possible explanations that might or might not expect this disproportion between what you have to expect. As our questioners have suggested, is it perhaps the orientation? After all, there are many phenomena in this universe, such as pulsars or blazars, that are only visible when the correct electromagnetic signal is "blasted" directly into our line of sight.

      Impression of an artist of an active galactic core. The supermassive black hole in the center of the accretion disk sends a narrow, high-energy matter beam perpendicular to the disk into space. A blazar some 4 billion light years away is the source of many of the highest energy cosmic rays and neutrinos. Only matter from outside the black hole can leave the black hole. Matter from the event horizon can ever escape.

      DESY, Science Communication Lab

      This is a clever idea, but it lacks a fundamental difference between the gravitational forces and the electromagnetic forces. In electromagnetism, electromagnetic radiation is generated by the acceleration of charged particles; In general relativity, gravitational radiation (or gravitational waves) is generated by the acceleration of massive particles. So far so good.

      But in electromagnetism there are both electrical and magnetic fields, and electrically charged particles generate magnetic fields. In this way, you can create and accelerate particles and radiation in a collimated manner. it does not have to be spherical. In gravitation, however, there are only gravitational sources (masses and energetic quanta) and the resulting curvature of space-time.

      If you have two gravitational sources (ie masses) that inspire and eventually merge, this motion causes the emission of gravitational waves. A gravitational wave detector, while not intuitive, is sensitive to these waves as a function of 1 / r and not 1 / r ^ 2 and can see these waves in all directions, regardless of whether they are in the face. on or edge-on or somewhere in between.

      NASA, ESA, and A. Feild (STScI)

      As it turns out, it does not really matter if we see an inspiring and merging source of gravitational waves -on, edge, or angle; They still emit gravitational waves of measurable and observable frequency and amplitude. There may be slight differences in the strength and other characteristics of the signal that depends on orientation in our eyes, but gravitational waves are spherically propagated from a source that generates them, and can be seen from anywhere in the universe for so long. Your detector is sensitive enough ,

      Why are no gravitational waves from binary sources discovered in our own galaxy?

      It may surprise you to discover that there are binary mass sources. like black holes and neutron stars that are now orbiting and inspiring.

      From the very first binary neutron star system ever discovered, we knew that gravitational radiation carried energy away. It was only a matter of time before we found a system in the final stages of inspiration and fusion.

      NASA (L), Max Planck Institute for Radio Astronomy / Michael Kramer

      Long before gravitational waves were discovered directly, we saw what we considered to be an extremely rare configuration: two pulsars orbiting each other. We observed how their pulse time varied in a way that showed their orbital decay due to gravitational radiation. Since then, many pulsars have been observed, including several binary pulsars. In either case, in which we could measure it accurately enough, we see the orbital decay, which shows that they emit gravitational waves.

      Similarly, we have observed X-ray emissions from systems that suggest that this is the case of a black hole in the middle. We've also found that although they're not talked about so often, they are binary X-ray systems in which two black holes orbit each other and emit X-rays that show the masses of both components.

      LIGO and Virgo have discovered a new population of black holes whose masses are larger than those previously observed with X-ray alone (violet). This graph shows the masses of all ten safe binary black hole fusions detected by LIGO / Virgo (blue) along with the neutron star neutron star fusion (orange). LIGO / Virgo should see several mergers per week with the sensitivity upgrade this week.

      LIGO / Virginia / Northwestern Univ./Frank Elavsky

      These systems are:

      • Rich in Milky Way,
      • Inspire and radiate gravitational waves to save energy,

      • which means using gravitational waves certain frequencies and amplitudes through our detectors,
      • with the sources producing these signals, which one day merge and complete their fusion. 19659049] But we have not observed them in our ground-based gravitational wave detectors. There is a simple, uncomplicated reason for this: Our detectors are in the wrong frequency range!

        The sensitivities of a variety of gravitational wave detectors, old, new and proposed. Pay special attention to Advanced LIGO (in orange), LISA (in dark blue) and BBO (in light blue). LIGO can only detect events with low mass and short period. Low noise, low noise observatories are required for either more massive black holes or for systems that are at an earlier stage of gravitational inspiration.

        Minglei Tong, Class.Quant.Grav. 29 (2012) 155006

        Erst in den letzten Sekunden der Koaleszenz fallen Gravitationswellen aus verschmolzenen Binärdateien in den LIGO / Virgo-Empfindlichkeitsbereich. In all den Millionen oder gar Milliarden von Jahren, in denen Neutronensterne oder Schwarze Löcher sich gegenseitig umkreisen und sehen, wie ihre Umlaufbahnen abnehmen, tun sie dies bei größeren radialen Abständen, was bedeutet, dass sie länger dauern, um sich gegenseitig zu umkreisen, was niedrigere Frequenz-Gravitationswellen bedeutet. 19659004] Der Grund, warum wir heute keine Binaries in unserer Galaxie sehen, ist, dass die Arme von LIGO und Jungfrau zu kurz sind! Wenn sie Millionen von Kilometern lang wären und nicht viele, sondern viele Reflexionen hätten, hätten wir sie schon gesehen. So wie es jetzt aussieht, wird dies ein bedeutender Fortschritt von LISA sein: Sie kann uns diese Binärdateien zeigen, die in der Zukunft zusammengeführt werden sollen, und sogar vorhersagen können, wo und wann es geschehen wird!

        Die drei Raumsonden von LISA werden es tun in Bahnen angeordnet werden, die eine dreieckige Formation bilden, mit einem Mittelpunkt von 20 ° hinter der Erde und einer Seitenlänge von 5 Millionen km. Diese Figur ist nicht maßstäblich. LISA ist empfindlich für viel niedrigere Frequenzquellen als LIGO, einschließlich zukünftiger Fusionen, die LIGO eines Tages zu sehen bekommen wird.

        NASA

        Es stimmt: Während der Zeit, in der LIGO und Virgo tätig waren, haben wir dies nicht getan Fusionen von Schwarzen Löchern oder Neutronensternen in unserer eigenen Galaxie gesehen. Das ist keine Überraschung. Die Ergebnisse unserer Gravitationswellen-Beobachtungen haben uns gelehrt, dass es in jedem Jahr irgendwo rund 800.000 Schwarz-Loch-Binärdateien im gesamten Universum gibt. Aber es gibt zwei Billionen Galaxien im Universum, was bedeutet, dass wir Millionen von Galaxien beobachten müssen, um nur ein Ereignis zu erhalten!

        Aus diesem Grund müssen unsere Gravitationswellenobservatorien empfindlich auf Entfernungen reagieren Milliarden Lichtjahre in alle Richtungen gehen; Ansonsten gibt es einfach nicht genug Statistiken.

        Die Reichweite von Advanced LIGO und seine Fähigkeit, verschmolzene Schwarze Löcher zu erkennen. Obwohl die Amplitude der Wellen um 1 / r abfällt, nimmt die Anzahl der Galaxien mit der Lautstärke zu: [3].

        LIGO Collaboration / Amber Stuver / Richard Powell / Atlas des Universums

        There Es gibt viele Neutronensterne und Schwarze Löcher, die sich im ganzen Universum umkreisen, auch hier in unserer eigenen Milchstraße. Wenn wir nach diesen Systemen suchen, entweder mit Radiopulsen (für die Neutronensterne) oder Röntgenstrahlen (für die Schwarzen Löcher), finden wir sie in großen Mengen. Wir können sogar die Beweise für die Gravitationswellen sehen, die sie emittieren, obwohl die Beweise indirekt sind.

        Wenn wir empfindlichere niederfrequente Gravitationswellenobservatorien hätten, könnten wir möglicherweise die von Quellen in unserer eigenen Galaxie erzeugten Wellen entdecken direkt. Wenn wir jedoch ein echtes Fusionsereignis erhalten wollen, sind diese selten. They might be aeons in the making, but the actual events themselves take just a fraction of a second. It&#39;s only by casting a very wide net that we can see them at all. Incredibly, the technology to do so is already here.


        Send in your Ask Ethan questions to startswithabang at gmail dot com!

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