(Image credit: NASA, ESA, C. Pallanca and F. Ferraro (University of Bologna) and M. van Kerquik (University of Toronto); editing: G. Kober (NASA/Catholic University of America))
A new deep space image shows a distant globular cluster of densely packed stars filled with stellar bodies like a swarm of glittering bees swarming around a cosmic hive.
The image taken by the Hubble Space Telescope focuses on the globular cluster NGC 6440, located in the constellation Sagittarius, about 28,000 light-years from Earth.
Such globular clusters usually appear at the edge of galaxies and consist of hundreds of thousands or millions of stars separated by an average distance of about one light year.
On the subject: The best images of the Hubble Space Telescope of all time!
While a light-year distance may seem like anything but “densely packed,” consider that the closest star to the Sun is Proxima Centauri, which is more than 4 light-years away. This is less than the average distance between stars in the Milky Way, which is 5 light years.
The stunning image is yet another example that Hubble can still deliver goods, even as its more powerful compatriot, the James Webb Space Telescope, has garnered attention since it began transmitting stunning space images back to Earth in July. 2022.
The Hubble image of NGC 6440, which was discovered by astronomer William Herschel in 1786, is the result of five separate Hubble observations of the globular cluster. However, four of these programs do not concern the buzzing of the star bees of this space hive.
Rather, they are focused on studying the much more exotic objects hidden within a globular cluster, its population of rapidly spinning neutron stars or pulsars.
NGC 6440 is home to at least eight pulsars, rapidly spinning neutron stars with magnetic fields a quadrillion – a thousand trillion – times stronger than Earth’s, that emit powerful beams of radiation as they spin.
Like all neutron stars, pulsars form when the cores of massive stars can no longer resist the internal pressure of gravity. This results in a complete gravitational collapse that compresses the mass around the mass of the Sun and more down to a width no larger than the width of a city here on Earth.
This means that neutron stars are made up of the densest material in the universe, a teaspoon of which weighs 4 billion tons, the equivalent of 10,000 Empire State Buildings.
In April 2022, astronomers discovered the latest additions to this population, two new millisecond pulsars in the cluster, designated NGC 6440G and NGC 6440H.
The incredibly dense composition is not the only extreme characteristic of NGC 6440’s millisecond pulsars. This type of neutron star gets its name from the fact that their rotation period is less than 30 milliseconds. Some have even been found with a rotation period of up to 1.4 milliseconds. This means that a millisecond pulsar can rotate between 2,000 and 43,000 times per minute.
Scientists believe these extreme neutron stars get their incredible spin rates when neutron stars form in binary systems and start accreting material from their stellar companion. When this donor material falls on a neutron, it also accumulates angular momentum and “unwinds”.
The millisecond pulsars NGC 6440G and NGC 6440H in the globular cluster NGC 6440 are believed to have rotation periods of 5.22 ms and 2.85 ms. This means that NGC 6440G rotates approximately 11,500 times per minute, while NGC 6440H rotates 21,050 times per minute.
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