# Tag Info

43

Energetic neutrinos have been observed from the core of a supernova (SN 1987A). The inferred temperature at the "neutrinosphere" is about 4 MeV (equivalent to 50 billion K - ($5\times 10^{10}$ K, Valentim et al. 2017). Hence it is observable and has been observed. The very centre of the proto-neutron star that is responsible for the neutrino emission is ...

22

Note that while we haven't observed anything even close, there is a theorized Absolute Hot along the lines of absolute zero. Its theorized value is ~ $1.416 \cdot 10^{32}$ Kelvin. Above this temperature, it would be impossible to pump more energy into a system, even gravitationally. That gives an upper bound on the maximum temperature we could measure.

15

Under General Relativity (GR) alone, a Black Hole's (BH's) event horizon is a point of no return -- anything that passes through the event horizon is lost and gone forever, and nothing comes out. Hence, under GR alone, BHs are utterly black and don't have a temperature at all. This is why the absorption of radiation (or anything else) by a BH doesn't raise ...

13

Before I start, I'll admit that I've criticized the question based on its improbability; however, I've been persuaded otherwise. I'm going to try to do the calculations based on completely different formulas than I think have been used; I hope you'll stay with me as I work it out. Let's imagine that Lucifer becomes a main-sequence star - in fact, let's call ...

10

This is a really hard question to answer as Carl Witthoft alludes to. The main problem is that there is no way you can finagle putting at atmosphere around the Sun and have it extend to the Earth. It would be wildly unstable and no matter what happens, the general result will be an explosion of energy that kills the Earth. And you can't really say you're ...

10

Well first thing's first: You would disintegrate. At the temperature of the Sun, most of the molecules that make up our bodies could not even survive, that is why we would not only fry and die, we would really disintegrate (all the molecules breaking apart, leaving only loose atoms). Let's now pretend heat doesn't exist. This is what would happen. First, ...

9

The real reasoning has nothing to do with some civilization "deliberately" hiding its radio emissions. Rather, the problem is that we can not expect some other civilization to do something we would not do ourselves. It makes no sense whatsoever to radiate large amounts of energy into space when there exist other, more economical alternatives. Radio ...

9

As far as I understand it, the heat death of the universe is a consequence of entropy, not expansion. All processes result in the shifting of some energy to higher entropy. Though the observable universe is an open system, the entire universe is an isolated system, so as more and more energy gets shifted to higher entropy over time the universe will ...

7

I think it's a fun question, if impossible. The only way to turn Jupiter into a star that's even remotely practical is to add to it's mass. Ignoring brown dwarfs that are very limited in energy output, to get a red dwarf going, you'd need to add at least 75-80 or so Jupiter masses. (a bit more than 24,000 earth masses). You'd want to add a fair ...

7

From a physics perspective From a physics perspective an object is a star when it is undergoing nuclear fusion, generally of hydrogen atoms at its core, this is regardless of its temperature! A star is not determined by its temperature, it is instead determined by it's internal processes. This does mean that if Jupiter began nuclear fusion it would be ...

6

Ignoring the impossibility of Jupiter going solar: Assume that Jupiter turns into duplicate of the Sun in terms of energy output. Energy transmitted to the earth follows an inverse-square law. Since Jupiter is, at best, 4 times farther from the Earth than the Sun, Jupiter will supply the Earth with, at most, 1/16 the energy that the Sun supplies, for an ...

6

Does the Earth receive any heat at all from the millions of other Stars in our Galaxy ? Effectively, no. Stars are too few and far between. Qualifying that "effectively, no": From http://stjarnhimlen.se/comp/radfaq.html#10, the stellar magnitude from total starlight is -5. Compare that to the -26.7 magnitude of the Sun as viewed from the Earth. That ...

6

Stars do not get hot because of nuclear fusion, they become hot enough to sustain nuclear fusion and this process maintains their temperatures. Nuclear fusion actually stops a star getting hotter. Protostars (before nuclear fusion) get hot because of a well known statistical relationship between the gravitational potential energy of a gas and the internal ...

5

I'm not sure what you mean by "heating effect". The amount another body is heated by a star with luminosity $L$ is quantified by its effective temperature: $$T_{eff}=\left(\frac{L(1-a)}{16\pi\sigma D^2}\right)^{1/4}$$ where $a$ is the albedo, $D$ is the distance to the other body, and $\sigma$ is the Stefan-Boltzmann constant. If the luminosity is given, ...

5

First, let's get a bit of background. "Absolute hot" is the concept that a maximum temperature exists. It describes your question exactly. For a long time, no one was able to figure out whether an absolute hot exists, but in the 20th century major revolutions in theoretical physics gave us answers. "Absolute hot" isn't the name of the hottest temperature, ...

5

Yes, the Earth does receive energy from the stars, but not much. The effective temperature of the night sky is about 3 Kelvin which is not much more that that of the cosmic microwave background at 2.7 Kelvin. The difference being due to the total energy of starts etc.(room temperature is ~295 kelvin) The coldness of the night sky is interesting in itself ...

5

In reality, Jupiter doesn't have nearly enough mass to initiate stellar ignition or sustain it if we could somehow start it going. Even the smallest star would require on the order of some 80 to 90 times the mass of Jupiter just to put out a faint red glow. Even to become a brown dwarf proto-star, Jupiter would require a mass increase on the order of at ...

5

Your argument (large temperature leads to greater mixing) is correct so long as there are no other large scale forces acting on the system. This isn't true in planet formation, because gravity plays a very important role. I'm not an expert on planet formation, but I think the argument goes something like this: As a planet forms from material from the ...

5

Star temperature is an interesting question since temperature varies a lot in a star. I think that the more relevant temperature to this question is the core temperature of the star: a star is born when it starts to burn hydrodgen in its core. Finally, hydrogen begins to fuse in the core of the star, and the rest of the enveloping material is cleared ...

4

The average surface temperature on Venus is 462 °C. You would need a temperature above 800 °C before you would notice any light. Added: Here are some calculated radiation outputs of the surface temperature of Venus, a 1000 °C black body and the sun.

4

It's due to Hawking radiation, a black body radiation due to quantum effects near the event horizon of black holes and named after Stephen Hawking that predicted this phenomena. From the same Wikipedia article: Hawking radiation reduces the mass and the energy of the black hole and is therefore also known as black hole evaporation. Because of this, ...

4

Sorta depends -- you can't have a uniform density atmosphere, so to reach something close to one standard atm. near Earth's orbit (which, BTW would wreak havoc with orbital stability in the first place due to drag), the density would have to be something horrible nearer to the Sun. This would be an excellent xkcd what-if question if phrased more along the ...

4

According to this paper, there are various but enough good estimations for the temperature gradient of the Martian soil. Note, direct measurements will we have first with the next Martian lander, the InSight: Image from here The for us important part of this estimation is this: Depth penetration of the annual temperature wave at $120^\circ E, > 20^\... 3 Roughly speaking, the moon's orbit has a semi-major axis of about 400,000 km. The semi-major axis of the Earth's orbit is 149.6 million km. The intensity of sunlight received by the Moon depends on the inverse of the square of the distance, so the difference amounts to$((1.496e8 + 4e5)/(1.496e8 - 4e5))^2\$ = 1.011, or about 1%. So, not very much. The ...

3

You got some very good answers already. I just want to point out this: The "temperature" of a black hole is more like just "a way of speaking". It's not temperature as normally understood. There is this process called the Hawking radiation where vacuum near a black hole produces a stream of particles, borrowing energy from the black hole's gravity to ...

3

Sun-Earth distance: 1AU Earth-Jupiter distance (at the conjunction): 4AU So Lucifer will be four times farther than Sun when it is nearer (six times when it is farthest), and at the same time it is a thousand times smaller. This is approx 40 times more light than full moon concentrated in a tiny point on sky.

3

You seriously cannot expect the sun to have a layer that would contain some of its harmful radiation. Sun consists of a plasma and is not solid. Learn more about its structure here. Magnetic field is a kind of layer you might think of apart from all gases and energy it radiates. But that is harmful and not protective for us. It is highly unlike earth which ...

3

If you're ruling out the big bang, then the most extreme releases of energy in our universe should be cases of runaway gravitational collapse. There is a rigorous theorem in general relativity (Penrose singularity theorem) showing that these will generically lead to the creation of singularities. For realistic gravitational collapse, it's expected that in ...

2

As other answers have said, the definition of a "star" is generally taken to be an object that is undergoing sufficient hydrogen fusion to reach an equilibrium between energy produced by fusion and the energy it is radiating. The exact definition varies, but does not affect this answer much. When "stars" are young, they are large, their cores are too cool ...

2

Can the release of gravitational energy during planet formation in principle (is there enough) explain this much heat Planets in general can have internal heat sources (like radioactive breakdown or a complex hot core). During planetary formation there are thought to be multiple collisions with large proto-planets before things settle down to a more-or-...

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