At the Birth of Creation - HD 150283

Most amateur astronomers love to boast about the furthest thing they've either seen or imaged in the sky, so how about spending a glance or two taking in the oldest object up there you're likely to ever see? I'm talking about the blue-white subgiant star HD140283 in the constellation Libra. HD140283 is an extremely metal-poor visitor to our neighborhood from the galactic halo (its inclined orbit about the Milky Way's core causes it to pass through the spiral arms twice per revolution), and is currently a mere 190 light years away.

HD140283 has been baffling astronomers for more almost 2 decades now, ever since its age was calculated back in the year 2000 to be approximately 16 billion years - in other words, older than the universe itself! Well... thanks to Hubble, we have now refined those earlier estimates downward, and the star is currently thought to be 14.5 billion years old, plus or minus 0.8 billion years. This is one case where that "plus or minus" turns out to be extremely important! Subtracting the full uncertainty factor from the estimate gives us an age of 13.7 billion years, i.e., about as old as the universe itself. HD140283 must therefore be one of the very first stars ever to have formed.

Indeed, HD140283, now affectionately nicknamed "Methuselah" by those studying it and officially the oldest known star in the universe, fits the expectations of what such a star would look like. Its metallicity (the percentage of a star's mass made up of elements heavier than hydrogen or helium) is only about 1/250th of the sun's. Recall that the younger a star, the higher its heavy element content, due to "seeding" from preceding generations of stars gone supernova. (It is believed that the early universe contained no heavy elements whatsoever.)

Astronomers believe that HD140283 did not form in the Milky Way, but is instead a survivor of a long-lost dwarf galaxy that was sucked into and absorbed by our own galaxy about 12 billion years ago. Its highly elliptical orbit within the halo is testimony to this long-ago cataclysm. At the moment, HD140283 is passing through our sun's spiral arm at a speed of more than 800,000 miles per hour - so fast that it can actually be seen to change position against the background stars in Hubble images taken only a few hours apart!

At magnitude 7.2, HD140283 should be an easy binocular object, but is best seen through your telescope. WARNING! Starhop instructions follow! Start by locating the constellation Libra, and identify the two brightest stars, Zubeneschamali (mag 2.6) and Zubenelgenubi (mag 2.7) (Don't you just love those names?), a.k.a., Beta and Alpha Librae. Making a rough equilateral triangle with these two stars is the magnitude 3.9 Gamma Librae, over to the left. Using a line between Gamma and Beta Librae as the hypotenuse of a yet smaller right triangle, you can then locate the magnitude 4.6 star 37 Librae, which would mark the point where our imaginary 90 degree angle would be. (This second triangle would be hanging off to the left of the first one.) From here it is an easy star hop of approximately three full moons leftward and slightly down to our target, HD140283. There is no other star in the immediate vicinity even approaching this one in brightness, so there should be little difficulty in making a positive identification.

Just remember when observing this "dot" that you are looking back to the very beginnings of our universe. Quite a thought.