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27

The most likely scenario is that an asymmetry in the supernova explosion imparts momentum to the proto neutron star at its core. The issue is not settled. A recent study by Verbunt et al. (2017) models the speed distribution of young pulsars as the sum of two Maxwellian distributions, one with an average speed of $\sim 130$ km/s and the other with an ...


18

Out of 100 pulsars, how many will have a beam that crosses the Earth? About twelve. "The beaming fraction f , that is the mean value of the fraction of observable pulsars or the mean probability of observing a normal pulsar, is 0.124 ± 0.004." M. Kolonko et al.: On the pulse-width statistics in radio pulsars


17

The key is to compare the range of pulsar periods and ther behaviour with the typical dynamical timescales of stars. Pulsar periods range from just less than $10^{-3}$ s to $\sim 10$ s. And $\dot{P}$ is positive - the periods are getting longer for most pulsars (and all of them that aren't in binary systems). The dynamical timescale is $\tau \simeq (G\bar{\...


17

The probability of seeing pulsed emission from a neutron star is simply the fraction of the sky covered by the beam, i.e. the beam solid angle divided by $4\pi$ steradians. The angle swept out on the sky by a pulsar with an emission cone of width $\rho$ turns out to be $$\zeta=4\pi\sin^2\left(\frac{\rho}{2}\right)$$ covering a fraction of the sky $$f=\frac{\...


14

It's generally dictated by how massive the star is. Remember what a pulsar is, it's a very rapidly rotating, highly magnetized neutron star. Neutron stars are a category of objects which have masses between 1.4 and 3.2 solar masses. This is the end stage of stars which are not massive enough to form black holes (they're held up by neutron degeneracy ...


13

It is believed that old pulsars may have their rotational axes closely aligned with their magnetic field. This would happen over a timescale of $\tau\sim10^7$ years (Lyne & Manchester (1988)). There are three sets of phenomena driving the dynamics of the alignment (Casini & Montemayor (1998)): Short-term ($\sim50$ days) variations caused by glitches ...


12

Your question is too general, you need to get to specific examples. First, very few neutron stars are pulsars. Pulsars are either a brief phase during a pulsar's spin-down at the start of a neutron star's life, or they are the product of the spin-up of a neutron star in a binary system. Most neutron stars fall in neither of these categories. A standard ...


8

Yes. In terms of pulsar timing measurements, this is a massive effect! A +/- 30 km/s doppler shift changes the pulsar frequency by +/- 1 part in 10000. This sounds small, but the accumulated phase shift over many periods is readily apparent. In addition, the light travel time across the solar system has to be taken into account, as well as the Earth's ...


8

It is thought that all neutron stars are pulsars when they are first born, as all spin extremely rapidly and have strong magnetic fields shortly after birth, arising from their dramatic collapse from a few Earth-sized massive star core into a city-sized neutron star. Conservation of angular momentum means that an initially slow-rotating core becomes a ...


8

All pulsars are observed to slow down gradually,albeit with a wide range of rates.The following diagram,known as the $\dot{P}-P$ diagram for pulsars illustrates this.The crab pulsar yes indeed would be a bad choice as a clock due to it's high $\dot{P}$. But there are pulsars to the bottom left of the diagram which have periods of the order of milliseconds(...


8

They don't need to be pointed exactly at us, since the angular beam radius is a few degrees (Pulsar Astronomy, P. 212) but there is a portion that we can't detect, described by a beaming factor (P. 211): The larger beamwidth at higher energies can be seen in these graphs: R. N. Manchester We mostly can't see "ordinary neutron stars". "neutron stars ...


7

The first thing you need to recall is that electromagnetic waves do carry momentum as well as energy. This shows up in effects like light pressure. Specifically a photon of wavelength $\lambda$ carries momentum $h/\lambda$. In and of itself, that doesn't answer your question though, since you are asking about the rotation of the pulsar, and changed to its ...


7

Yes. One of the features that helps this scenario is the gravitational bending of light close to the neutron star, which allows for a larger fraction of the surface to be visible at a given time. Many pulsars have double-peaked light curves, for example here's the light curve of the Crab Pulsar. In the pencil beam model these peaks correspond to the beams ...


7

The Vela Pulsar (PSR J0835-4510 or PSR B0833-45) is a radio, optical, X-ray- and gamma-emitting pulsar associated with the Vela Supernova Remnant in the constellation of Vela. First line of the Wikipedia entry on the Vela pulsar. It's obviously much more spread out and diffuse than the Crab nebula because it occurred more than 10 times as long ago. Here it ...


6

Yes, it is correct. Consider the classic example of a (say) $1000$ Hz siren on an ambulance approaching you. Once a single wave is produced, the source moves towards you before the next wave is produced. The wavelength of the sound waves in the air is reduced, so the frequency you hear is increased. Simple, basic Doppler shift... But consider the case ...


5

Short answer is: yes. Longer answer is: correcting for the time dilation effects of Earth moving around the Sun's gravitational potential is actually relatively standard in almost all branches of astronomy. To the point where running that correction is a sentence in a paper (sometimes less), and is probably why you had trouble Googling for it. (I'll caveat ...


5

The magnetic field of a star is not entirely a result of the global spin of the star. The global spin is part of it, but there are other mechanisms as well. Within the star, there are convection zones, meridional flow, etc. http://solarscience.msfc.nasa.gov/dynamo.shtml All these flows generate their own field components. The overall field is simply the ...


5

The endpoint in the lives of massive stars between about 10 and 25 solar masses is thought to be a core-collapse supernova that produces a condensed remnant called a neutron star. The lower mass limit for neutron star progenitors is reasonably well known and due to the evolutionary paths taken by stars of differing masses. Below 10 solar masses it is ...


5

The pulsar map used by Pioneer and Voyager is a diagram of the position of the Sun relative to 14 galactic pulsars. It encodes their positions, distances, and pulse periods, which in theory makes it a decent tool for identifying where the Solar System is (although there are some issues with it). To make a similar map for an arbitrary point in the galaxy, you'...


5

The optical pulsations of the Crab pulsar have been studied closely since 1969. The observations are actually not that difficult (I did some myself with a photoelectric photometer as a student) and have been achieved with a variety of technologies. A paper by Fordham et al. (2002) slices and dices the Crab pulsar's pulse shape into fine time and spectral ...


5

Pulsars are precise because... in essence, there isn't much to cause them to be imprecise. It's as if you spun a top in intergalactic space and left it there for a hundred years - it would likely still be spinning (at pretty much the same rate). In essence, pulsars are super-dense neutron stars that are rotating really fast, and their emission axis happens ...


5

NICER observations of PSR J0030+0451 in x-rays show hot spots clustered near one pole. The hot spots are presumed to be the termination of the active magnetic field lines, so there is really no magnetic "axis". The field is more complicated. First surface map of a pulsar


5

Two things would be required. First, your line of sight would have to be close to looking along the magnetic axis of the neutron star. Second, that magnetic axis would have to be closely aligned with the rotation axis of the pulsar. If both of these are pseudo-randomly distributed and the pulsar beam is narrow, then this is inherently a very unlikely ...


4

Let us suppose that the pulsar is spinning down at a uniform rate. So it has a period $P$ and a rate of change of period $dP/dt$ that is positive and constant (in practice there are also second, third, fourth etc. derivatives to worry about, but this doesn't change the principle of my answer). Now let's assume you can measure the period very accurately - ...


4

I asked Google for this, and the first link that I followed took me to Wikipedia, where I found the basics as: A pulsar (portmanteau of pulsating star) is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. This radiation can only be observed when the beam of emission is pointing toward the Earth, much the way a ...


4

How LIGO, LISA, etc. Detect Gravitational Waves The point of instruments like LIGO and LISA is to measure time-varying changes in the distance within different arms of the instrument. In the case of an arm oriented in the direction of an incoming gravitational wave (GW), the length of the arm will increase and decrease, while an arm oriented perpendicular ...


4

the signal period of known pulsars is 1 ms-15 s (0.07-1,000 Hz since F=1/T). That's the frequency of how often the signals occur, not the frequency of the waves they emit. Just compare it to a lighthouse, which has a signal period of a few seconds but a wave frequency of $10^{15}$ Hz. The first known pulsars, for example "Little Green Man" or PSR B1919+21, ...


4

Several pulsars have double-peaked profiles: you get two peaks per rotation, with one peak stronger than the other. An example of this is the Crab Pulsar. This suggests that at least some pulsars have two beams. Remember that the gravitational bending of light in the vicinity of the neutron star makes it possible to see a larger fraction of the surface, ...


4

The magnetic and rotational axes don't have to be exactly at 90 degrees to each other to see both beams. They only need be approximately at 90 degrees (depending on the 'opening angle' of the emission cone). So there are plenty of pulsars that satisfy this and have two peaks in their profiles (when we observe their emission) that are approximately half a ...


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