On 23/06/2017 04:06, wlandsman wrote:
On Wednesday, June 21, 2017 at 9:27:03 PM UTC-4, jacobnavia wrote:

Sure, but excuse me, a star like the sun, yellow, main sequence star, is
5 Gy or more old. All stars in that galaxy (z=2.1) can't be older than
2Gy. To keep things in order, galaxy formation is questioned, but not
the big bang theory.

The published paper
( https://arxiv.org/ftp/arxiv/papers/1706/1706.07030.pdf ) gives an
observed spectroscopic age of the galaxy of log[Age(yrs)] = 8.97
(+0.26,-0.25) or between 500 million and 1.7 billion years. This
is comfortably within its cosmological age at a redshift of z=2.15
of 3 billion years.

(Yes, the Sun is currently a 4.6 billion year old yellow main
sequence star. But yellow, main sequence stars can be much younger
than the Sun. For example, 4 billion years ago, the Sun was a
600 million year old yellow main-sequence star.)

A bit dimmer when younger but otherwise still main sequence and yellow.

The tricky questions are "why did it stop making new stars?" or put
another way "where did all the dust and gas go?". Swept clean by a
galactic collision perhaps or related to its unusually high spin?

--
Regards,
Martin Brown