The biggest planet in the universe

What is the biggest planet in the universe?
Where is it?
Is it mainly made of iron?

 

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It's the planet Arbuckle, in the Hoag's Object galaxy and we don't know its composition because its sky is made of concrete.

 

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To be realistic, use our solar system as a model. Jupiter is mostly H and He like most of the universe.

 

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TrES-4b is an extrasolar planet, and one of the largest exoplanets ever found

 

It took less than a minute to type in an appropriate search term and come up with e.g.:
http://pono.ucsd.edu/~adam/papers/physicstoday.pdf
From that it can be gathered there is no such thing as 'the largest planet in the universe' but rather an essentially continuous spectrum from 'super Jupiters' to 'brown dwarfs'. Any delineation being somewhat arbitrary. And as already mentioned, composition won't be iron to any significant degree.
I'll bet just the act of getting responses to your latest 'inquiring' thread has given you another buzz.

 

If the Earth has the same radius as Jupiter, and same mass too, means that the center has big empty space.
Then we will have same g = 9.81 m/s^2.
Like this, the Earth will have plenty of land for us to use.
This will be a perfect planet.
Of course the jupiter-sized Earth must have different revolution speed to maintain comfortable temperature for night and day.
If the Earth is at the current location from the Sun, but the radius is the same as Jupiter, can you calculate its revolution speed to maintain current temperature?

 

Nope.

No it won't.

No, a Jupiter-like planet will not have any land to use.

Nope.

Everything you concluded is wrong. Planets can't have a "big empty center space." A Jupiter sized Earth of the same mass as Earth will not have the same gravitational acceleration as Earth does. The speed of revolution does not determine average temperature, nor would you have to spin at a greater speed (in terms of length of day/night cycle) to have a similar diurnal temperature range as Earth,

 

garbage exchemist?

 

do u mean the Earth's dimension is the optimal for hosting lives?

 

Earth's dimensions are optimal for its mass.

 

Maintain the Earth's mass, increase its radius.
GMm/r^2 still applied, we still feel the same gravity, right?
Then we have more surface area to use.

 

Not double, maybe increase the radius by 20%.
The surface will increase by a factor (1.2)^2 = 1.44.
We have extra 44% of land area to use.

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Why would it be land area that increases?

 

Centrifugal force. Not saying the earth is by any means hollow

 

If you spun it fast enough, that would cause the equator to blow off into space while the poles collapsed inward. Centrifugal force doesn't work evenly on a sphere.

If you actually have the ability to build something that big, build a Ringworld instead. Engineering issues are similar.

 

UY Scuti is the biggest star?
1700 times the width of the Sun.
But is it only full of gas, no solid?

 

Unknown at this point.

A lot depends on how one defines "planet". If a planet gets large enough, maybe several times the mass of Jupiter, it starts to slide into "brown dwarf star" territory. These are objects classified as "stars" rather than "planets", but that aren't massive enough to sustain fusion reactions at their core.

There are probably lots of these. Probably some of them orbit around more massive stars and satisfy that criterion for being a "planet".

So my opinion is that the dividing line between "planet" and "star" is kind of vague and arbitrary and there are probably countless objects that straddle that gap.

Probably not. I'd guess that these kind of objects are more along the lines of our solar system's gas giants. They may indeed have iron cores though.