I Speediest Exoplanet System

[Tom.G]

TL;DR Summary

1.2 million miles per hour!

'The planetary system is thought to move at least 1.2 million miles per hour, or 540 kilometers per second.'

“We think this is a so-called super-Neptune world orbiting a low-mass star at a distance that would lie between the orbits of Venus and Earth if it were in our solar system,” said Sean Terry

https://www.nasa.gov/universe/nasa-scientists-spot-candidate-for-speediest-exoplanet-system/

Here is a link to the full article:
https://iopscience.iop.org/article/10.3847/1538-3881/ad9b0f/meta

(the links on the NASA site sometimes don't work.
seems to be an advertising link getting in the way).

Cheers,
Tom

 

[Greg Bernhardt]

What factors are in play for what contributes to a systems speed?

 

[Tom.G]

Same as a figure skater doing a spin-in-place. Arms extended the spin is slower rotation than arms at side of body. (Constant energy)

I surmise if it is a captured planet that was passing by and was captured, that the approaching trajectory placed it close to the star, the gravitational attraction lead to a high approach and orbital speed.

I'll leave it to those more qualified to explain the situation of 'a bunch of rocks coalescing to a Sun and planets.'

Cheers,
Tom

 

[DaveC426913]

Is this about orbital speed of the planet? Or relative motion of the system?

Same as a figure skater doing a spin-in-place. Arms extended the spin is slower rotation than arms at side of body.

Did you just explain the correlation between orbital distance and orbital velocity ... to @Greg Bernhardt??


The paper seems to be talking about high-velocity stars in the galactic bulge.

 

[Juan Gilberto]

My biggest curiosity is why that star system started spinning so fast. Obviously, it's due to its early formation, but what kind of interaction caused that? Did it have a companion back then that heavily interacted and caused it?

 

[DaveC426913]

My biggest curiosity is why that star system started spinning so fast. Obviously, it's due to its early formation, but what kind of interaction caused that? Did it have a companion back then that heavily interacted and caused it?

Again, I think they're talking about high velocity star systems, not high velocity planetary orbits.

It's hard to tell; they seem to be way more interested in talking about their experimental setup than they are in the actual results.

 

[Ibix]

Dave is correct, the velocity being measured is that of the lens system (which is probably a small star and a large planet), not the components of the system relative to one another. Section 4.1.2 in the IOP Science link in the OP states this.

 

[snorkack]

But that’s just its 2D motion; if it’s also moving toward or away from us, it must be moving even faster.

A lot of distant objects possess radial velocity but not proper motion or parallax. How does this object have a good tangential speed but no radial speed?

 

[mfb]

It has a radial speed, we just can't measure that with microlensing.

Close encounters in binary systems can easily accelerate a star to hundreds of kilometers per second, but that process will generally strip all planets. If this system exists (see the paper for caveats) this might be a stray star from outside the galaxy.

 

[snorkack]

It has a radial speed, we just can't measure that with microlensing.

Close encounters in binary systems can easily accelerate a star to hundreds of kilometers per second, but that process will generally strip all planets. If this system exists (see the paper for caveats) this might be a stray star from outside the galaxy.

Do we have a good idea of its actual position relative to the Milky Way centre, and of the local escape speed? It is already well over 500 km/s at Sun!

 

[mfb]

We know the direction, we know the distance, so yes. You can calculate where in the Milky Way it is based on that.

 

[snorkack]

We know the direction, we know the distance, so yes. You can calculate where in the Milky Way it is based on that.

I was worried because the direction to the star is close to the direction of Milky Way centre and so is the distance.
Taking the difference of two close and independent measurements amplifies the error.
Could the star system be just a halo star? On a high eccentricity orbit with apoapse far from Milky Way centre but periapse near the centre, and currently near the centre?
How strongly is the halo concentrated near the Milky Way centre?
Consider that for a test mass on a low periapse orbit in a field of a large mass, its speed grows as 1/√R, and therefore the time it spends in any equal volume like a cubic lightyear decreases as √R - but the volume of a shell with thickness dR shrinks as R². As incoming halo objects concentrate from all directions towards the centre, their density at any volume at a given time should therefore grow as 1/R√R - unless the bulge has an appreciable mass relative to the centre, in which case the speed would grow slower and the concentration of density towards the centre would be even closer to 1/R²
What does the bulge consist of? Is it just the concentration of halo, of high apoapse low periapse orbits now near their periapse and thus high speed? Or does the bulge consist of objects on low apoapse, low speed orbits?