How Could a Moon Become a Sun?

[bcohen1]

Hi everybody,

I apologize if this has been asked already - I searched for a similar topic to no avail. My question regards something touched upon briefly in Olaf Stapledon's book Star Maker. Stapledon writes of interstellar travel being acheived by detaching a planet from a solar system and hurtling it toward a nearby star. So that the inhabitants of said planet don't freeze to death, they would somehow illuminate a satellite that would then orbit the planet, acting as a tiny mobile sun.

My initial question is, how would you achieve this hypothetically? Would you irridiate the moon somehow? What kind of reaction would you need to create?

Furthermore, if (again, extremely hypothetically) our sun became dimmer and we wanted to illuminate our own moon without necessarily detaching the Earth from our solar system, what would the effect be? How would an illuminated moon (for lack of a better term) affect our tide, planetary wobble, gravitational attraction to the other planets, etc.

I'm just really curious about this and I know it's pretty far out, but I'm not a scientist of any kind and I don't really know any scientists, so I was hoping that somebody here might be able to help. Thanks in advance for any thoughts and I hope you all have a nice day!

Kind regards,
Ben Cohen

 

[mgb_phys]

You can turn the moon (or anything else) into a star by just dumping mass on it.
As the mass increases the pressure at the centre increases until a thermonuclear reaction starts and you have a sun.
The minimum mass for a star is probably around 5% of the mass of the sun. The moon is only about 1% of the mass of the Earth and the Earth is only 1/millionth the mass of the sun, so you are going to have to drop a lot of mass on the moon (about 10^29kg) to make it a star.

Needless to say it wouldn't be very pleasant being that close to even a very small star - so you would also want to move the moon away a little.

 

[bcohen1]

Thank you so much for your reply! I have a few followup questions, if you don't mind.

First of all, how much mass could you dump onto the moon before it started to adversely affect the Earth in some way (gravitational, tidal or otherwise)?

How much energy would the moon output if you were to dump this maximum 'safe' amount of mass onto it?

How might you convey this mass to the moon? Would you have to create some kind of heavy element there?

Finally, if you didn't want to turn the moon into a full blown star, would there be a way to dump just enough mass into it to turn it into some kind of molten satellite that could act as a supplement to the sun if the sun was to dim, or if we weren't able to receive the same output from the sun that we do now, or some like scenario?

Sorry if these questions don't make any sense, and thanks again for any help.

 

[mgb_phys]

First of all, how much mass could you dump onto the moon before it started to adversely affect the Earth in some way (gravitational, tidal or otherwise)?

Tricky - it depends what you mean by affect.
I really don't know, I imagine any significant mass increase (10% or so) would have an effect. The tides affect us now, would a 1m higher tide affect us - it would flood a few cities?

How much energy would the moon output if you were to dump this maximum 'safe' amount of mass onto it?

5% of the solar mass is the minimum for a star to turn on. Less than this you don't have a nuclear reaction at all.
You would still generate some heat just from the compression as you dump more mass onto it (a bit like air in a bike pump getting hot). Jupiter is about 50x too small to be a star but still generates more heat than it receives form the sun.

How might you convey this mass to the moon? Would you have to create some kind of heavy element there?

Getting it there, and finding somewhere to get it from is of course tricky - but ultimately any mass will do. The sun and Jupiter are mostly made of hydrogen - the lightest element.
But the density of the sun and Jupiter are only a bit more than water, if you had unlimited supplies of lead or depleted uranium or something you could make a much smaller denser object that would heat up.

Finally, if you didn't want to turn the moon into a full blown star, would there be a way to dump just enough mass into it to turn it into some kind of molten satellite that could act as a supplement to the sun if the sun was to dim, or if we weren't able to receive the same output from the sun that we do now, or some like scenario?

Yes, as with Jupiter as you dump mass it beings to compress it gives off heat. Since it is still pretty cold this is in the form of infrared and so wouldn't light up the sky.
I'm guessing that you wouldn't get a high enough temperature form an object to glow in the visible until you dumped enough mass on it that it became a star.