A southie looks north, I

[Weltevreden SA (Dana)]

Recently I revisited some old friends in the northern sky. My observing latitude is 33° south. Seeing was around 1 arcsec with lazy, slow waves, and 6th mag visual. Equipment couldn’t be simpler: a 6-inch AstroTele refractor on an alt-az, and 2 eyepieces.

First up, NGC 2419, the Intergalactic Tramp in Lynx. Has anything in the sky ever enjoyed a jauntier name? At a sky elevation of about 17° it was visible in direct as a round patch 4’ dia. with a thin halo embracing a uniform 3’ core—about what it looks in a 4-inch in 45° N skies. It is nearly twice as remote as the Magellanics, and yet visually brighter than any LMC globular. To us it appears less luminous than M13 in Hercules, but its actual luminosity surface density is six times greater. Since globulars have a flat mass-luminosity ratio, that means 2419 has six times as many stars, and M13 is no featherweight. N2419 is very old as globulars go, born 13.2 billion years ago within a dark matter “minihalo” of roughly 1 billion solar masses. (In dark matter circles, a billion solar masses qualifies as “mini”.) In those dim reaches of bleakness when the universe was young, “mini” blobs of dark matter interacted in the same bumptious way that large hydrogen clouds interact today. N2419 was born from two dark matter blobs located very far from other dark matter blobs.

That is why N2419 is so far and so alone. Their merger spanning a million years set up turbulence shocks out of which a rapidly infalling starburst shrank. In the very much denser, hotter universe of half a billion years after the Big Bang, a simple term like “turbulence” has huge ramifications—Mach 90 gas velocities are not an uncommon figure when astronomers study shocks big enough to mold a million-mass globular. While most globulars take a few million years to form in their entirety, in early giants like N2419, ten million solar masses of gas can reach nearly protostellar densities before the first stars form—and then they burst into life like a firecracker string, half a million stars in a hundred thousand years. (Our Milky Way makes a piffling 2 to 3 stars every million years.) NGC 2419’s stars were pristine hydrogen and helium, roughly 0.07 % of the metallicity of the sun. From that plus N2419’s present population, astronomers calculate a 900,000 solar mass first generation, followed by a much smaller second generation 250 million years later. Sheer chance favoured N2419 to a birth very far from other huge stellar masses being born at the same time. Two of these became the cores of M31 and the Milky Way. Life ever after was so tame that N2419 departs from a perfect sphere by only 0.03%—that’s rounder than Neptune. It is a globular Hawaii on the cruise to Andromeda Australia. Wave as you pass, it won’t return to its present position again for 3.1 billion years. By then we and our Sun will have rotated around the galaxy ~125 times, which will be roughly 250 Galactic spiral arm crossings. There will be no Lynx, no us, and not much Sun, but N2419 will hardly have turned a hair.