Universe Today

Some of the oldest structures in the Milky Way are the globular clusters. Ancient collections of millions of stars, that have held together by mutual gravity over billions of years. But new data collected by NASA’s Chandra X-Ray Observatory casts doubt on their “ancient nature”. They might be surprisingly less mature than astronomers previously believed.

According to conventional wisdom, globular clusters pass through three phases of evolution in the development of their structure: adolescence, middle age, and old age. Keep in mind, we’re talking about the age of the cluster here, not the age of the individual stars in the cluster.

One way to calculate the age of a cluster is to look for the presence of binary X-ray sources. These happen when two stars get so close to one another that they begin to transfer mass. The transfered material piles up into an accretion disk around one star, which can blaze brightly in the X-ray spectrum. Globular clusters should form these X-ray binaries in their middle age, and then lose them again as they reach old age.

Recent images from NASA’s Chandra X-Ray Observatory revealed the number of bright X-ray sources in two globular clusters: NGC 6397 and NGC 6121. While they were expecting to see less double stars in NGC 6397, it was just the opposite.

Instead of most globular clusters being in their middle ages, astronomers are starting to think that many are in an adolescent stage of evolution. When astronomers surveyed 13 globular clusters, 10 were in adolescence and only 3 were middle aged.

With so many clusters in the earlier stags of their evolution, the later stages must take much longer to reach than astronomers previously believed. Even though the clusters are already billions of years old, they’ve barely reached their prime.

Original Source: Chandra News Release

Once the planet Uranus was discovered, astronomers have suspected that there are probably more planets in the Solar System. Astronomers used Newtonian mechanics to predict Neptune from its perturbations of Uranus’ orbit. German astronomer Gottfried Galle found Neptune exactly where calculations predicted it should be.

Now that they knew the method worked, astronomers set about finding other planets beyond Neptune. In the late 19th century, astronomers were starting to suspect that another body was pulling on both Uranus and Neptune, and so they tried to calculate its position, and then go look for it.

Percival Lowell, a wealthy Bostonian who founded the Lowell observatory in Flagstaff, Arizona, took up that search. He searched from 1905 all the way up to his death in 1915, and he never found it.

The job then turned to a young astronomer named Clyde W. Tombaugh – a 22-year old Kansas farm boy. Tombaugh spent the better part of a year staring at two photographic plates capturing the same region of sky at two different points in time.

Using a tool called a blink comparator, Tombaugh finally turned up images of Pluto moving in 1930. It turns out there had been evidence of Pluto in earlier photographs, but nobody had noticed it yet.

As the discoverers, Tombaught and his team were given the honor of naming Pluto. In the end, they settled on the name Pluto, suggested by a British school girl.

In the beginning of the 20th century, astronomers studied the orbit of Neptune and calculated that there must be another planet in the outer reaches of the Solar System that was pulling at the planet with its gravity. Percival Lowell, who was made famous by his “discovery” of canals on Mars, coined the term for this theoretical object: Planet X.

Lowell performed two searches for Planet X, but failed to turn up the object. He revised his predictions for the location of Planet X twice, and failed to find it. Ironically, two faint images had been recorded on photograph plates at the Lowell observatory, but Lowell didn’t recognize them.

Lowell’s observatory continued to search for Planet X up until his death in 1916. So the task fell to Clyde Tombaugh. Tombaugh’s job was to systematically observe pairs of photographs taken of the night sky. He used a machine called a blink comparator, which flashed two images of the same region of the sky. Any moving objects, like asteroids or undiscovered planets, would appear to change in position from one image to the next.

On February 18, 1930, Tombaugh finally turned up the object he was looking for, and announced that he had discovered Planet X, later renamed to Pluto.

Astronomers have been searching for additional planets beyond Pluto ever since, hoping to find the elusive Planet X. Japanese astronomers have predicted that an object between the size of Mars and Earth could be out at the end of the Kuiper Belt – a region known as the Kuiper Cliff, at 55 astronomical units from the Sun.