Stella: Sol's Sister

By Clark M. Thomas
May 10, 2014


Stars such as our own (Sol) do not appear from nothing in the past. Each new star has had a gassy/dusty stellar nursery. Unlike human families, stars don't have just one or two siblings. They typically have dozens or hundreds that form from chemically rich clouds. Such a cloud of gas and enriched dust 4.5 billion years ago was our birth nursery.

New stellar families express themselves thereafter as star clusters, mostly as open clusters that don't have a large amount of gravitational cohesiveness, due to their small numbers. After some millions of years the siblings wander away from each other following interactions with other gas clouds, and even interactions with dark matter. Only a very few open stellar families survive beyond a billion years.

Several of the Big Dipper stars are included in the nearest open cluster. Because it is so close to us it doesn't look to us like a cluster. Slightly farther away is the loose Hyades cluster. Farther still is the visually tighter Pleiades, which is notable for the gas we can see therein. See this link.

Globular clusters, many of which are ten billion years old, are among the more ancient structures in our visible universe. Because of their much larger populations, globular clusters have plenty of cohesive gravity to maintain their ball shape for the long run. Some of the largest even host small black holes. It is likely that most globular clusters formed from the accumulation of a number of loose clusters in the early universe. Gravity formed their round shapes, similar to what we see with Ceres, the largest asteroid, but not with the less massive asteroids.

The universe's very earliest dust clouds were all low in metallicity. That elemental simplicity made it impossible to form planets such as ours, and certainly impossible to support life. Those phenomena awaited later generations of dust clouds enriched by supernovae which had created complex and heavy atoms. After nine billion years the universe had birth clouds rich enough in the heavy atoms we would need to build life.

A lot of celestial shuffling has happened in the last 4.5 billion years. Where have all our stellar relatives gone? There are two ways to track them down. First, we can now track in reverse stars over billions of years as they orbited the core of our Milky Way. Second, each birth cloud has its own "finger print" of trace chemicals. In our cloud's case we are looking at candidate stellar spectra for rare barium and yttrium in the proportion we see in Sol's spectrum.

Drum roll, please.... And the winning candidate is a star in the constellation Hercules, like ours in color, with a visual magnitude 6.46, HD162826. This number is not a pretty name for a pretty star in our family. Astronomers should come up with a better name. I propose we also call her "Stella," in honor of Stella Kowalski, in A Streetcar Named Desire.

Although there are other family stars in our galaxy, Stella is exciting because it is likely the most nearby, and only 15% more massive than Sol, and because it has the same metallicity that our solar system sports. Astronomers have not found any "hot Jupiters" near it, and the hunt is just beginning for Earth-sized rocky planets in its Goldilocks zone. It's 110 light years away, so we won't be going there any time soon. Nevertheless, we can see it now with binoculars:

The primary source article for this essay is see this link. This Discovery News article has a finder map of sorts for binoculars. That map is a worthless tease, because you can "see" this star, and still not be able to distinguish Stella from similarly bright nearby stars.

Therefore, starting with the article-supplied map of this region of Hercules, I have prepared for you a representation of what you would see with a pair of binoculars at 10 power. Note that Stella is in the center (shown as the diamond), and it is slightly less bright than its two visually close companions, all three forming an arc.

Note too that this orientation is only rotationally accurate for this calendar date and time, as circumpolar stars appear to move around Polaris, the north star, every day. This rotation rule applies whether you are using your naked eye, binoculars, or any telescope. However, the spatial relationship of the three stars to each other does not change, even though their collective orientation rotates. The three together form a curve, with Stella being the least bright, and with star 90 Hercules on the opposite end of the three-stars curve being the most bright.

The second image below is what you would see with a Newtonian reflector telescope at 56 power. This type of scope visually reverses objects in the eyepiece north and south, and also east and west, due to the path light takes inside the instrument. By comparison, binoculars, as shown above, show the same "normal" relationship that the naked eye sees.

While you are outside, use those binoculars to check out some more of Nature's amazing beauties. I recommend the great globular star cluster, M13, also in Hercules. Then be amazed at all you can see in the Milky Way galaxy plane from a moonless dark-sky site. Look toward the constellation Cygnus.