Dead Star Set to Escape the Milky Way

slackah wrote to mention a NewScientist.com article discussing a fast-moving stellar corpse on its way out of our galaxy. From the article: "The object, called B1508+55, is a rotating neutron star, or pulsar. It is the superdense core of a massive star that exploded as a supernova about 2.5 million years ago. The explosion seems to have ejected the pulsar with such force that it will eventually escape the Milky Way entirely, says team member Shami Chatterjee, an astronomer with NRAO and CfA."

Re:Galaxies must be a lot more dynamic than I thou

[darmey]

Not millions - the Milky Way has only about hundrend of thousands of lightyears in size. So at least some of our ancestors could see it when it was in our galaxy for sure. If neanderthalls are our ancestors, of course.

Thats nothing unususal

[imsabbel]

Those neutron stars are the product of stellar cores collapsing into a neutron star (and then sheding the outer hull thats impacting on the core rebounce shockwave in a class II supernova).

Now if such a collapse isnt absolutly symetrical, there will be higher spherical hermonics in the neutron core oszillation, and thus the impact of the hull on the core will give it a random impuls vector (the first harmonic being the 2 hemispheres oszilating with 180degree phase difference).

The observation of those fast moving neutron stars helped the understanding of this processes, as there isnt much that can accelerate them after their creation to this speeds.

A common speed of a class2 supernova product is in the 100-1000 km/s range (about 2 orders of magnitures lower than the speed of the the ejected hull, thus the visible SNR still seemingly have the neutron star in the center), which is way enough for most to leave our galaxy (300 or so is needed)

Re:How is this possible?

[Burz]

Many supernovas are asymmetric. The net effect is that the remaining core receives a sideways "kick".

Re:How is this possible?

[imsabbel]

The main point is: the core isnt EXPLODING, its COLLAPSING to a neutron star. The "explosion" is just a rebounce off the core (_slightly_ simplified :) ).

After the collapse, the kinetic energy of the quasi free falling neutron matter will overcompress the neutron star core, and then it will oscillate.

As the collapse istn something perfectly symetrical, there will be significant amplitude of the first harmonic of the oscillation. Thus (for example) the matter hitting the star on one hemisphere will have the core expanding in their direction with quite some speed, while the other side will see it receeding). As the impact isnt very long, there wont be time to average out. In the moment the hull impacts, the core will "push" itself away from that quasi-spherical shell thats hitting it.

(you have to remember: there is significant mass in that shell. Only a small part of the star actually ends of in the neutron star, so there IS enough mass in the hull for conservation of momentum)

Re:It can't be a space station.

[Cee]

It's too big to be a space station.

Don't say that, a neutron star [wikipedia.org] has a diameter of about 25 km. :)

Re:Amazing

[eggstasy]

Galaxies aren't circular, they are elliptical, and accurately calculating the circumference of an ellipse is very different from 2*pi*r.
http://en.wikipedia.org/wiki/Circumference [wikipedia.org]
Wikipedia confirms the poster's numbers BTW.
http://en.wikipedia.org/wiki/Milky_Way [wikipedia.org]

Re:Stellar probes for dark matter

[schwanerhill]

B1508+55 is a massive radio emitting object which is boldly going into the intergalactic space where all that putative dark matter is supposed to be. If its path bends we might end up discovering a "dark galaxy".

Indeed, pulsars are used to probe the interstellar medium to get at how much mass is tied up in ionized hydrogen, which scatters incident radio waves, causing scintillation which can be observed with a radio telescope. (Scintillation is the same effect the Earth's atmosphere has on visible light from stars, known as twinkling.) One of the ways we estimate the electron density in interstellar space is by comparing the dispersion of the pulsar signal to the distance to the pulsar. (This assumes you can get an accurate measurement of the distance, which is hard and uncertain for all but the most nearby pulsars.) There aren't great constraints on how much mass is tied up in interstellar gas, although it's not a terribly hot prospect for the missing baryonic mass.

There are about 40 known pulsars that are substantially above the plane of the milky way (galactic altitude > 3 kpc or 9000 light years; this pulsar is 2.4 kpc away, according to the paper, for an altitude of 1.9 kpc). Most of these are in globular clusters or the Large and Small Magellenic Clouds, two small, nearby galaxies that orbit the Milky Way. What's remarkable about this pulsar is that it formed in the galactic plane and was kicked up that high.

Pulsars typically move at velocities of ~100 - 500 km/s, so they cover a lot of space quickly, which lets you see the changes in the scintillation pattern on solar system size scales over the course of a few months. If you want to look at big scales, you look at many different lines of sight (i.e. many different pulsars).

(Yes, I am a pulsar/interstellar medium astronomer, or at least a grad student who works in this area and knows very little.) ;)

Re:How is this possible?

[Yazeran]

An other explanation of a fast star leaving the galaxy is a 'slingshot' trajectory close to some other star. One of the stars would loose energy (and fall towards the galactic center) and the other would gain energy and possibly achieve escape velocity.

The slingshot principle has been used for a number of spacecrafts and there is a number of trajectories which could transfer momentum between two objects traveling in a common gravity well (e.g. galaxy or solar system).

Yours Yazeran

Plan: To go to Mars one day with a hammer.