APOD: Messier 4 (2024 Nov 29)

[APOD Robot]

Messier 4

Explanation: Messier 4 can be found west of bright red-giant star Antares, alpha star of the constellation Scorpius. M4 itself is only just visible from dark sky locations, even though the globular cluster of 100,000 stars or so is a mere 5,500 light-years away. Still, its proximity to prying telescopic eyes makes it a prime target for astronomical explorations. Recent studies have included Hubble observations of M4's pulsating cepheid variable stars, cooling white dwarf stars, and ancient, pulsar orbiting exoplanet PSR B1620-26 b. This sharp image was captured with a small telescope on planet Earth. At M4's estimated distance it spans about 50 light-years across the core of the globular star cluster.

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[johnnydeep]

Here it says the exoplanet orbits a pulsar, but the exoplanet link says the star type is unknown. Are there different types of pulsars? And another link says the planet orbits a white dwarf / pulsar binary!

[Christian G.]

Here it says the exoplanet orbits a pulsar, but the exoplanet link says the star type is unknown. Are there different types of pulsars? And another link says the planet orbits a white dwarf / pulsar binary!

Yes, apparently this lucky planet has two stars to itself, but sadly both are dead! Seriously though, what an exotic environment... As for pulsars, I don't know about this particular one but the only different "type" I see besides normal ones are millisecond pulsars, and globular clusters are the perfect breeding ground for them (and for blue stragglers too, for similar reasons).

[Ann]

I didn't reply before because the picture was too yellow for me. But Johnny's question and Christian's answer are interesting.

In the dense pinball machine of a globular cluster, planets are lucky to stay in orbit around their parent stars in the first place.

Click to play embedded YouTube video.

Star cluster pinball machine.

Pinball machine. Credit: Votpuske

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There are two things to bear in mind about globular clusters and why they can certainly contain exotic stars. First, these clusters started out absolutely huge, and because they were so huge, they started out with mammoth stars inside them. Huge clusters always do.

A near-infrared closeup of the central part of R136. At birth, the three brightest stars each weighed more than 150 times the mass of the Sun. The most massive star, known as R136a1 and located at the centre of the image, has been found to have a current mass of 265 times that of the Sun. It also has the highest luminosity, at some seven million times greater than the Sun. Credit: ESO/P. Crowther/C.J. Evans

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R136 in the Tarantula Nebula, the largest very young cluster in the Local Group. Credit: NASA, ESA, F. Paresce (INAF-IASF, Bologna, Italy), R. O'Connell (University of Virginia, Charlottesville), and the Wide Field Camera 3 Science Oversight Committee

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The mammoth stars of the newborn globular clusters may easily have been weirdos themselves. But more importantly, absolutely all kinds of stellar interactions are going on inside globulars.

Two types of stellar weirdos that are either definitely or probably produced by stellar interactions are V838 Mon, which may have eaten one of its planets, and millisecond pulsars that were spun up by a bloated companion.

Click to play embedded YouTube video.

Creation of a millisecond pulsar.

Evolution of V838 Mon. Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA); Acknowledgment: H.E. Bond (STScI)

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What if there is interaction between an already pretty exotic star and another star or a planet? I guess it's not always so easy to classify every star in a globular cluster.

Ann

[johnnydeep]

Ann, about that video about millisecond pulsars. When the narrator says "a pulsar lasts" for millions of years or billions of years, what does that mean? Surely the neutron star itself will last essentially forever - as a neutron star. Does he just mean that the neutron star will stop being detectable as a pulsar, because of diminishing radiation, or maybe that the spin will slow to a virtual stop, or both?

[Chris Peterson]

Ann, about that video about millisecond pulsars. When the narrator says "a pulsar lasts" for millions of years or billions of years, what does that mean? Surely the neutron star itself will last essentially forever - as a neutron star. Does he just mean that the neutron star will stop being detectable as a pulsar, because of diminishing radiation, or maybe that the spin will slow to a virtual stop, or both?

Pulsars slow down because they are radiating energy. Once they drop below a certain speed the mechanism that creates the EM beam turns off. That takes 50 or 100 million years or so.

[johnnydeep]

Ann, about that video about millisecond pulsars. When the narrator says "a pulsar lasts" for millions of years or billions of years, what does that mean? Surely the neutron star itself will last essentially forever - as a neutron star. Does he just mean that the neutron star will stop being detectable as a pulsar, because of diminishing radiation, or maybe that the spin will slow to a virtual stop, or both?

Pulsars slow down because they are radiating energy. Once they drop below a certain speed the mechanism that creates the EM beam turns off. That takes 50 or 100 million years or so.

Thanks. So could a millisecond pulsars last billions of years or is 100 million years the max, even for one rotating 1000 times a second?

[Chris Peterson]

Ann, about that video about millisecond pulsars. When the narrator says "a pulsar lasts" for millions of years or billions of years, what does that mean? Surely the neutron star itself will last essentially forever - as a neutron star. Does he just mean that the neutron star will stop being detectable as a pulsar, because of diminishing radiation, or maybe that the spin will slow to a virtual stop, or both?

Pulsars slow down because they are radiating energy. Once they drop below a certain speed the mechanism that creates the EM beam turns off. That takes 50 or 100 million years or so.

Thanks. So could a millisecond pulsars last billions of years or is 100 million years the max, even for one rotating 1000 times a second?

The oldest known pulsar is 200 million years old. Millisecond pulsars lose energy not just via the emission of EM, but also by gravitational waves, so they slow faster, at least initially. I don't think anything could push their lifetimes out much beyond that. Most pulsars are young, most stop radiating when they're just a few tens of millions of years old, the few that are 100 million years old or more are seen as rare and exotic.

[johnnydeep]

Pulsars slow down because they are radiating energy. Once they drop below a certain speed the mechanism that creates the EM beam turns off. That takes 50 or 100 million years or so.

Thanks. So could a millisecond pulsars last billions of years or is 100 million years the max, even for one rotating 1000 times a second?

The oldest known pulsar is 200 million years old. Millisecond pulsars lose energy not just via the emission of EM, but also by gravitational waves, so they slow faster, at least initially. I don't think anything could push their lifetimes out much beyond that. Most pulsars are young, most stop radiating when they're just a few tens of millions of years old, the few that are 100 million years old or more are seen as rare and exotic.

Except that the narrator in Ann's video says that a pulsar that has been "spun up" by the accreting gas from a red giant companion, and whose magnetic field has been diminished by that same process, can last for billions of years? Unless that accretion process itself can last billions of years and so keep spinning up the pulsar?

[Chris Peterson]

Thanks. So could a millisecond pulsars last billions of years or is 100 million years the max, even for one rotating 1000 times a second?

The oldest known pulsar is 200 million years old. Millisecond pulsars lose energy not just via the emission of EM, but also by gravitational waves, so they slow faster, at least initially. I don't think anything could push their lifetimes out much beyond that. Most pulsars are young, most stop radiating when they're just a few tens of millions of years old, the few that are 100 million years old or more are seen as rare and exotic.

Except that the narrator in Ann's video says that a pulsar that has been "spun up" by the accreting gas from a red giant companion, and whose magnetic field has been diminished by that same process, can last for billions of years? Unless that accretion process itself can last billions of years and so keep spinning up the pulsar?

No idea. But that sounds like something that might fall into the "exotic" category, not anything typical of pulsars, millisecond or not.

[johnnydeep]

The oldest known pulsar is 200 million years old. Millisecond pulsars lose energy not just via the emission of EM, but also by gravitational waves, so they slow faster, at least initially. I don't think anything could push their lifetimes out much beyond that. Most pulsars are young, most stop radiating when they're just a few tens of millions of years old, the few that are 100 million years old or more are seen as rare and exotic.

Except that the narrator in Ann's video says that a pulsar that has been "spun up" by the accreting gas from a red giant companion, and whose magnetic field has been diminished by that same process, can last for billions of years? Unless that accretion process itself can last billions of years and so keep spinning up the pulsar?

No idea. But that sounds like something that might fall into the "exotic" category, not anything typical of pulsars, millisecond or not.

Ok, perhaps not every video on YouTube is 100% accurate in all respects.

[Chris Peterson]

Except that the narrator in Ann's video says that a pulsar that has been "spun up" by the accreting gas from a red giant companion, and whose magnetic field has been diminished by that same process, can last for billions of years? Unless that accretion process itself can last billions of years and so keep spinning up the pulsar?

No idea. But that sounds like something that might fall into the "exotic" category, not anything typical of pulsars, millisecond or not.

Ok, perhaps not every video on YouTube is 100% accurate in all respects.

What? Say it ain't so!