Normal Stars & Star Clusters

In some ways, star clusters are like giant families with thousands of stellar siblings. These stars come from the same origins – a common cloud of gas and dust – and are bound to one another by gravity. Astronomers think that our Sun was born in a star cluster about 4.6 billion years ago that quickly dispersed.

By studying young star clusters, astronomers hope to learn more about how stars – including our Sun – are born. NGC 6231, located about 5,200 light years from Earth, is an ideal testbed for studying a stellar cluster at a critical stage of its evolution: not long after star formation has stopped.

The discovery of NGC 6231 is attributed to Giovanni Battista Hodierna, an Italian mathematician and priest who published observations of the cluster in 1654. Sky watchers today can find the star cluster to the southwest of the tail of the constellation Scorpius.

For decades, astronomers have known about irregular outbursts from the double star system V745 Sco, which is located about 25,000 light years from Earth. Astronomers were caught by surprise when previous outbursts from this system were seen in 1937 and 1989. When the system erupted on February 6, 2014, however, scientists were ready to observe the event with a suite of telescopes including NASA’s Chandra X-ray Observatory.

V745 Sco is a binary star system that consists of a red giant star and a white dwarf locked together by gravity. These two stellar objects orbit so closely around one another that the outer layers of the red giant are pulled away by the intense gravitational force of the white dwarf. This material gradually falls onto the surface of the white dwarf. Over time, enough material may accumulate on the white dwarf to trigger a colossal thermonuclear explosion, causing a dramatic brightening of the binary called a nova. Astronomers saw V745 Sco fade by a factor of a thousand in optical light over the course of about 9 days.

Illustration Credit: NASA/CXC/M.Weiss

A new study using data from NASA's Chandra X-ray Observatory and ESA's XMM-Newton suggests X-rays emitted by a planet's host star may provide critical clues to just how hospitable a star system could be. A team of researchers looked at 24 stars similar to the Sun, each at least one billion years old, and how their X-ray brightness changed over time.

Since stellar X-rays mirror magnetic activity, X-ray observations can tell astronomers about the high-energy environment around the star. In the new study the X-ray data from Chandra and XMM-Newton revealed that stars like the Sun and their less massive cousins calm down surprisingly quickly after a turbulent youth.

This artist's illustration depicts one of these comparatively calm, older Sun-like stars with a planet in orbit around it. The large dark area is a "coronal hole", a phenomenon associated with low levels of magnetic activity. The inset box shows the Chandra data of one of the observed objects, a two billion year old star called GJ 176, located 30 light years from Earth.

In the context of space, the term 'cloud' can mean something rather different from the fluffy white collections of water in the sky or a way to store data or process information. Giant molecular clouds are vast cosmic objects, composed primarily of hydrogen molecules and helium atoms, where new stars and planets are born. These clouds can contain more mass than a million suns, and stretch across hundreds of light years.

The giant molecular cloud known as W51 is one of the closest to Earth at a distance of about 17,000 light years. Because of its relative proximity, W51 provides astronomers with an excellent opportunity to study how stars are forming in our Milky Way galaxy.

A new composite image of W51 shows the high-energy output from this stellar nursery, where X-rays from Chandra are colored blue. In about 20 hours of Chandra exposure time, over 600 young stars were detected as point-like X-ray sources, and diffuse X-ray emission from interstellar gas with a temperature of a million degrees or more was also observed. Infrared light observed with NASA's Spitzer Space Telescope appears orange and yellow-green and shows cool gas and stars surrounded by disks of cool material.

In biology, "symbiosis" refers to two organisms that live close to and interact with one another. Astronomers have long studied a class of stars – called symbiotic stars – that co-exist in a similar way. Using data from NASA’s Chandra X-ray Observatory and other telescopes, astronomers are gaining a better understanding of how volatile this close stellar relationship can be.

R Aquarii (R Aqr, for short) is one of the best known of the symbiotic stars. Located at a distance of about 710 light years from Earth, its changes in brightness were first noticed with the naked eye almost a thousand years ago. Since then, astronomers have studied this object and determined that R Aqr is not one star, but two: a small, dense white dwarf and a cool red, giant star.

Although there are no seasons in space, this cosmic vista invokes thoughts of a frosty winter landscape. It is, in fact, a region called NGC 6357 where radiation from hot, young stars is energizing the cooler gas in the cloud that surrounds them.

This composite image contains X-ray data from NASA's Chandra X-ray Observatory and the ROSAT telescope (purple), infrared data from NASA's Spitzer Space Telescope (orange), and optical data from the SuperCosmos Sky Survey (blue) made by the United Kingdom Infrared Telescope.

Michael McCollough

We are pleased to welcome Dr. Michael McCollough as our guest blogger. Dr. McCollough is the first author of a paper that is the subject of our latest press release. He has spent the last 30 years working with and analyzing data from astronomical radio, optical, X-ray, and gamma-ray telescopes. Currently, he serves as an Archival Astrophysicist at the Chandra X-ray Center in Cambridge, Mass.

Throughout my career I have been a multi-wavelength astronomer. To fully understand astronomical objects, one must look across the electromagnetic spectrum (from radio waves to gamma-rays). Also throughout my career I have been doing spacecraft operations. Starting with NASA’s Hubble Space Telescope (before, during, and after launch), ROSAT, NASA’s Compton Gamma-Ray Observations with the Burst and Transient Source Experiment (BATSE), and currently with NASA’s Chandra X-Ray Observatory. It was when I was working with BATSE that I was introduced to Cygnus X-3. Discovering that high-energy X-rays (as seen by BATSE) were correlated with emissions in the radio.

We are pleased to welcome Nick Wright as our guest blogger. Nick is the lead author on a paper featured in our latest press release, about how magnetic fields are generated in stars. He is an astrophysicist working at Keele University in the UK. He completed his PhD at University College London before moving to the Smithsonian Astrophysical Observatory to study X-ray emission from both young and old stars. After almost 5 years working in the US he returned to England as a Royal Astronomical Society research fellow at the University of Hertfordshire and is now an Ernest Rutherford Fellow at Keele University. When not studying the stars or writing about them on his blog, Nick enjoys cooking, gardening and travelling.

Nick Wright Credit: Nick Wright

Magnetic fields in the Sun and Sun-like stars are generated by a dynamo, a process involving the rotation of the star as well as convection, the rising and falling of hot gas in the star's interior. Understanding the magnetic dynamo of our Sun is important because it is responsible for a lot of interesting and energetic solar phenomena, some of which can have a considerable impact on our Earth and the wider Solar System. The Sun's magnetic field is responsible for sunspots on its surface, the 22-year magnetic activity cycle (the "Solar cycle"), the Solar wind that pummels planets throughout our Solar System and the ejections of large quantities of plasma – a gas composed of free electrons and free atomic nuclei – known as coronal mass ejections. This ejected material can have a serious impact on Earth, resulting in geomagnetic storms that disrupt radio transmissions, damage satellites and electrical grids, as well as harm astronauts or even people flying in airplanes at high altitudes.

Young stars much less massive than the Sun can unleash a torrent of X-ray radiation that can significantly shorten the lifetime of planet-forming disks surrounding these stars. This result comes from a new study of a group of nearby stars using data from NASA's Chandra X-ray Observatory and other telescopes.

Researchers found evidence that intense X-ray radiation produced by some of the young stars in the TW Hya association (TWA), which on average is about 160 light years from Earth, has destroyed disks of dust and gas surrounding them. These disks are where planets form. The stars are only about 8 million years old, compared to the 4.5-billion-year age of the Sun. Astronomers want to learn more about systems this young because they are at a crucial age for the birth and early development of planets.

One of the most recognizable constellations in the sky is Orion, the Hunter. Among Orion's best-known features is the "belt," consisting of three bright stars in a line, each of which can be seen without a telescope.

The westernmost star in Orion's belt is known officially as Delta Orionis. (Since it has been observed for centuries by sky-watchers around the world, it also goes by many other names in various cultures, like "Mintaka".) Modern astronomers know that Delta Orionis is not simply one single star, but rather it is a complex multiple star system.