These brilliantly bright blue stars are part of the cluster NGC 2547. Located 1,500 light-years away from Earth, these are some of the newest stars in the galaxy, clocking in at just 20 to 35 million years old.
Admittedly, a few dozen million years probably sounds plenty old to you or me, but it's all a question of scale. Specifically, 20 million years is barely any time at all on a cosmic scale that measures the lifespan of a star like our Sun in the billions, not millions, of years. Indeed, 20 million years doesn't even make much of a dent even on a geological timescale — the continents were more or less in their current positions 20 million years ago, although some mountain ranges and other modern-day geological features were still in the process of forming.
Really, it's probably best to think of these stars on an evolutionary timescale. The asteroid impact that wiped out the dinosaurs predates these stars by at least 30 and possibly as much as 45 million years. These stars were born around the time monkeys and apes split into distinct groups. The youngest stars in these photos are only 5 million years older than the first hominids. The astronomers at the European Southern Observatory, who took this photo using their Wide Field Imager in Chile, offer one other possible way of thinking about the youth of these stars:
That doesn't sound all that young, after all. However, our Sun is 4600 million years old and has not yet reached middle age. That means that if you imagine that the Sun as a 40 year-old person, the bright stars in the picture are three-month-old babies. Most stars do not form in isolation, but in rich clusters with sizes ranging from several tens to several thousands of stars. While NGC 2547 contains many hot stars that glow bright blue, a telltale sign of their youth, you can also find one or two yellow or red stars which have already evolved to become red giants. Open star clusters like this usually only have comparatively short lives, of the order of several hundred million years, before they disintegrate as their component stars drift apart.
For more, including a look at the complete, uncropped image, check out the ESO website.