This brown dwarf should be a bit hotter, right?

[Themohawkninja]

I've been messing around in Space Engine, and I just came across a brown dwarf that is 0.278 AU from a type O2 V star (52500 K) and 6.935 AU from a type M1 Ia star (3550 K). The side of the brown dwarf that faces the O2 V star is bright white, and despite all of this, it is stated to only be 1200 K.

If such a system were real, shouldn't that brown dwarf at least be a bit hotter, if not nearly a red dwarf from all the thermal radiation?

P.S. If you want to check it out, the main barycenter is: RS 0-1-4-99-30770-0-0-1

[K^2]

I'm having hard time picturing an O2 main sequence star. That's already way off. But if there was one, it'd have to have magnitude of -10, at least. (That's the closest I can get to an O V star from the charts.) Making it about a million times more luminous than the Sun. So lets take 5x10³⁴W as a ballpark estimate. At 52,500K, that would require the star to be about 96 million km in diameter, which is already way larger than distance to the brown dwarf.

Basically, the whole system is total fiction. You can't orbit 0.278 AU from an O2 star.

[Themohawkninja]

I'm having hard time picturing an O2 main sequence star. That's already way off. But if there was one, it'd have to have magnitude of -10, at least. (That's the closest I can get to an O V star from the charts.) Making it about a million times more luminous than the Sun. So lets take 5x10³⁴W as a ballpark estimate. At 52,500K, that would require the star to be about 96 million km in diameter, which is already way larger than distance to the brown dwarf.

Basically, the whole system is total fiction. You can't orbit 0.278 AU from an O2 star.

I think by "distance" it was referring to the surface of the star, not the center.

[K^2]

I don't think it matters. Tidal forces, etc.

[Themohawkninja]

I don't think it matters. Tidal forces, etc.

So, your saying that the brown dwarf should have long since had it's gases either blown away from stellar winds and/or sucked into the star?

[K^2]

The whole scenario is kind of crazy to begin with. I don't know why there would be a brown dwarf right next to an O V. Main sequence stars are hot really early in their life. So I have no idea why there would even be a brown dwarf, but supposing it was a capture, they'd tear at each other. And to be honest, I don't know which one would be winning. A dwarf has advantage due to much higher density, so it might be the brown dwarf that would be stealing gas from the star. Either way, though, you aren't going to have a peaceful co-habitation. I mean, that's basically how novas happen.

[Themohawkninja]

The whole scenario is kind of crazy to begin with. I don't know why there would be a brown dwarf right next to an O V. Main sequence stars are hot really early in their life. So I have no idea why there would even be a brown dwarf, but supposing it was a capture, they'd tear at each other. And to be honest, I don't know which one would be winning. A dwarf has advantage due to much higher density, so it might be the brown dwarf that would be stealing gas from the star. Either way, though, you aren't going to have a peaceful co-habitation. I mean, that's basically how novas happen.

Brown dwarfs can't be that dense, because they are sub-stellar objects. Shouldn't their density lie somewhere between Jupiter and a red dwarf?

[K^2]

I would imagine so. Which is still rather dense compared to the outer layers of the star. Especially a young one with surface temperature of over 50,000K.

[astropapi1]

That title was unsetting...

Edited December 30, 2013 by astropapi1

[Themohawkninja]

I would imagine so. Which is still rather dense compared to the outer layers of the star. Especially a young one with surface temperature of over 50,000K.

I always thought that all main sequence stars were fairly dense, and they only get significantly less dense when they reach the red giant stage.

[K^2]

This is a bit out of my comfort zone, but it's my understanding that despite having a dense, massive core, the O V stars have a very low density outer shells, due primarily to high temperatures and immense amount of energy they radiate. The O V Wikipedia article gives the following useful bits of info.

These stars have between 15 and 90 times the mass of the Sun and surface temperatures between 30,000 and 52,000 K. They are between 30,000 and 1,000,000 times as luminous as the Sun.

The O2 would be on the hot, massive, luminous side of this spectrum. So it looks like I was right on the money with it being a million times more luminous. The article even links to BI 253 as an example of an O2 V. So these things do exist, it turns out. And the article on stellar evolution notes the following.

Extremely massive stars (more than approximately 40 solar masses), which are very luminous and thus have very rapid stellar winds, lose mass so rapidly due to radiation pressure that they tend to strip off their own envelopes before they can expand to become red supergiants, and thus retain extremely high surface temperatures (and blue-white color) from their main-sequence time onwards.

And everything points to the O2 V being in the 60-90 solar masses range, so it'd definitely fit in this category. Seeing how it's going to be losing atmosphere already, I can't imagine how putting a brown dwarf right next to it is going to do anything but make this way worse. On the other hand, having something with 60+ solar masses right next to a brown dwarf can't be good for the dwarf, either.

So I don't really know which is going to happen. If the dwarf is going to be stripping off the outer shells of the star. If so, will that make the dwarf go nova, or just slow it down enough to be consumed by the star. Or is the brown dwarf just going to be ripped apart by tidal forces and that'd be the end of it.

One thing I'm not picturing is the brown dwarf peacefully orbiting that star.

[Themohawkninja]

One thing I'm not picturing is the brown dwarf peacefully orbiting that star.

Gee... Now I kind of wish I had access to a supercomputer with a program to simulate ultra-realistic n-body, gas, and plasma physics just to see what would happen.