Chris Peterson wrote: ↑
Tue Jan 28, 2020 12:38 am
Guest wrote: ↑
Tue Jan 28, 2020 12:28 am
hollandinseattle wrote: ↑
Tue Jan 28, 2020 12:27 am
Has anybody done the math on this? If the the galaxy is 800,000 light years across, its circumference would be a staggering 502 TRILLION light years. Is this right or am I not carrying the one?
C = r(squared) x pi
C = πD. If it is 800,000 ly across (which I'm doubtful is accurate) its circumference is about 2.4 million ly. The formula you give is for area
(although the meaning of area is a bit ambiguous for something which is shaped like a combination of a spheroid and a disc).
And that area
would be 502 billion
square ly, not trillion
. (1 billion = 109
Visible disk (220,000 ly) of Andromeda Galaxy, vs halo (2 million ly).
Credits: NASA/STScI. Full size here.
As Chris said, it seems improbable that the radius of UGC 2885 is 800,000 light-years across. But its true radius does not appear to be well known. NASA/ESA
claimed that it is 2.5 times wider than the Milky Way (which would make it perhaps some 250,000 light-years across), whereas Wikipedia
wrote that it is 463,000 light-years across.
But UGC 2885 might actually be at least 800,000 light-years across, if we take its halo into account. Being an isolated galaxy in space, it is sure to have a halo. Our neighbour Andromeda, which is not isolated in space, has a huge halo. See the picture.
On a different note, different sources disagree on how wide the visible disk of Andromeda is. According to Wikipedia
, its diameter is 220,000 light-years, but according to NASA.gov
, its halo is just 6 times wider than its visible disk, even though the illustration at right suggests that the halo is 2 million light-years across.
In any case, if we include the halo of UGC 2885 its diameter might well be 800,000 light-years.