Polaris is the Closest, Brightest Cepheid Variable. Very Recently, Something Changed.

View from within the Polaris triple star system; artist's rendering. The North Star is labeled Polaris A. Credit: NASA/ESA/HST, G. Bacon (STScI)

When you look up in the night sky and find your way to the North Star, you are looking at Polaris. Not only is it the brightest star in the Ursa Minor constellation (the Little Dipper), but its position relative to the north celestial pole (less than 1° away) makes it useful for orienteering and navigation. Since the age of modern astronomy, scientists have understood that the star is a binary system consisting of an F-type yellow supergiant (Polaris Aa) and a smaller main-sequence yellow dwarf (Polaris B). Further observations revealed that Polaris Aa is a classic Cepheid variable, a stellar class that pulses regularly.

For most of the 20th century, records indicate that the pulsation period has been increasing while the pulsation amplitude has been declining. But recently, this changed as the pulsation period started getting shorter while the amplitude of the velocity variations stopped increasing. According to a new study by Guillermo Torres, an astronomer with the Harvard & Smithsonian Center for Astrophysics (CfA), these behaviors could be attributed to long-term changes related to the binary nature of the system, where the two stars get closer to each other, and the secondary perturbs the atmosphere of the primary.

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Neptune's Cloud Cover is Linked to the Solar Cycle

This sequence of Hubble Space Telescope images chronicles the waxing and waning of the amount of cloud cover on Neptune. Credits: NASA, ESA, Erandi Chavez (UC Berkeley), Imke de Pater (UC Berkeley)

Whenever Neptune reaches its closest point in the sky to Earth, its portrait is taken by the Hubble Space Telescope and other ground-based observatories. Watching the planet from 1994 to 2020, astronomers have made puzzling discovery.

The clouds in Neptune’s atmosphere appear to be to be linked to the solar cycle and not the planet’s cycle of seasons. The global cloud cover seems to come and go in a cycle that apparently syncs up with the Sun’s 11-year cycle, as it shifts from solar maximum to solar minimum or vice versa. This is surprising since Neptune is so far from the Sun and receives about 0.1% of Earth’s sunlight.

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Exoplanet Surveys are Leaning Towards the Possibility That our Solar System is… Normal

One of the unspoken caveats of most exoplanet discovery missions is that they only operate for a few years.  Such a short observing window means there are planets with longer orbital periods, usually further out from the star, that those surveys would completely miss.  Knowing this would be a problem, a team of astronomers arranged the California Legacy Survey three decades ago in order to monitor as many stars as possible for as long a time as possible.  Recently they released their first results, which show solar systems that are surprisingly like our own.

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Who was Gerard Kuiper?

Gerard Kuiper, founder of the Lunar and Planetary Laboratory. Credit: lpl.arizona.edu

In the outer reaches of the Solar System, beyond the orbit of Neptune, lies a region permeated by celestial objects and minor planets. This region is known as the “Kuiper Belt“, and is named in honor of the 20th century astronomer who speculated about the existence of such a disc decades before it was observed. This disc, he reasoned, was the source of the Solar Systems many comets, and the reason there were no large planets beyond Neptune.

Gerard Kuiper is also regarded by many as being the “father of planetary science”. During the 1960s and 70s, he played a crucial role in the development of infrared airborne astronomy, a technology which led to many pivotal discoveries that would have been impossible using ground-based observatories. At the same time, he helped catalog asteroids, surveyed the Moon, Mars and the outer Solar System, and discovered new moons.

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Grand Spiral Galaxy Graced By Faded Supernova

One of the most lovely deep space objects to observe is the grand-design spiral galaxy and there are few so grand as NGC 1637. Located in the constellation of Eridanus and positioned approximately 35 million light years away, this twisted beauty was home to a radical supernova event just 14 years ago. Now astronomers are taking a close look at the resultant damage caused by the stellar explosion and giving us some pretty incredible views of the galaxy as well.

When viewing NGC 1637, it seems as if the galaxy itself is evenly distributed, but take a closer look. In this image you will notice the spiral arm to the top left is much more openly constructed and stretches out a bit further than the more concentrated and stubby spiral arm to its opposite side. You will also notice the more compact arm has the appearance of being cut through its mid-section. In whole, this particular appearance is what astronomers refer to as a “lopsided spiral galaxy”.

Now, let’s talk about what happened to disturb the peace…

In 1999, high atop Mt. Hamilton and near San Jose, California, the Lick Observatory was busy utilizing a telescope which specialized in searching for supernova events. Low and behold, they discovered one… a very bright one located in NGC 1637. Like all astronomical observations, the call went out immediately to other observatories to confirm their find and to gather support data. As with most dramatic events, SN 1999em was quickly and thoroughly researched by telescopes around the world – its magnitude carefully recorded and the resultant fading meticulously accounted for as the years have passed.

Better to burn out than to fade away? There are very few things in our natural world which can match the violent beauty of a supernova event. When a star ends its life in this way, it goes out with a bang, not a whimper. For their cosmic finale, they briefly outshine the combined light of all the stars contained within the host galaxy. Like snowflakes, each supernova is unique and the cataclysmic star within NGC 1637 was eight times more massive than our Sun.

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This video sequence starts with a view of the bright constellation of Orion (The Hunter). As we zoom in, we focus on an adjacent region of the constellation of Eridanus (The River) and a faint glow appears. This is the spiral galaxy NGC 1637, which appears in all its glory in the final view from ESO’s Very Large Telescope. In 1999 scientists discovered a Type II supernova in this galaxy and followed its slow fading over the following years. Credit: ESO/Nick Risinger

Go ahead. Take another look. During the confirmation observing runs, astronomers also imaged SN 1999em with the VLT and this data was combined with the Lick Observatory information to give us the spectacular view above. Caught in the spiral arm are young stars singing the blues amidst ethereal gas clouds and veiling dust lanes. NGC 1637 isn’t alone, either… You’ll see line of sight stars and even more galaxies in the background.

No rust here…

Original Story Source: ESO News Release.