A colorized photo of a sunspot with the Earth shown for scale.

New results from three different studies indicate the Sun is likely entering a prolonged period of low activity, which will have a profound effect on the Earth. Solar scientists base their conclusion on weakening magnetic fields along the poles of the Sun and decreasing intensity of sunspots.

“The solar cycle may be going into a hiatus,” Frank Hill, associate director of the National Solar Observatory’s Solar Synoptic Network, said in a news briefing [June 14].

The studies looked at a missing jet stream in the solar interior, fading sunspots on the sun’s visible surface, and changes in the corona and near the poles.

“This is highly unusual and unexpected,” Hill said. “But the fact that three completely different views of the sun point in the same direction is a powerful indicator that the sunspot cycle may be going into hibernation.”

Since the 1800s, scientists have known that the Sun goes through a cycle in which the number of sunspots visible on the Sun’s surface gradually rises to a maximum and then falls to a minimum, repeating approximately every 11 years. Sunspots are dark patches on the surface of the Sun about the size of the Earth. They appear dark in photos of the Sun, because the plasma in sunspots is relatively cool (~4,500 K) compared with the plasma elsewhere on the surface of the Sun (~5,800 K). The key word is relatively — if you were so unwise as to point your telescope directly at a sunspot, you would still be blinded.

Sunspots usually appear on the surface in pairs, and that is because they are connected by magnetic field lines, which are created and altered by the roiling sea of plasma on the surface of the Sun. Magnetic field lines are kind of like rubber bands in that they can be twisted and stretched, and sometimes this twisting action causes magnetic field lines to get wound up and extend out from the surface of the Sun. Sunspot pairs are observed where the lines poke out from the surface (see below). The reason the temperature of sunspots is lower than the surrounding region is that the magnetic field lines prevent hotter plasma from flowing into those areas.

During the solar maximum, when the number of visible sunspots reaches a peak, the Sun’s magnetic field actually flip-flops. If you think of the Sun as sort of like a gigantic bar magnet, this means the south magnetic pole becomes the north magnetic pole, and vice versa. The Sun thus has a solar cycle that lasts about 22 years, since this is how long it takes for the Sun’s magnetic field to return to its previous polarity.

Solar scientists believe that the current maximum may be the last we’ll see for decades, and this has profound implications for the Earth’s climate. The sunspot cycle repeats fairly regularly, but the intensity of the sunspot cycle can change dramatically. In the late 1950s there was a particularly strong solar maximum, and in the period 1645 to 1715 there was virtually no sunspot activity at all. The latter period is referred to as the Maunder minimum (after the astronomer who discovered it in observational records¹). The significance of the Maunder minimum is that it coincided with a prolonged period of exceptionally cold weather in Europe and North America, referred to as the Little Ice Age. This is part of a general trend of colder periods coinciding with solar minima. If we are entering another prolonged period devoid of solar maxima, it is likely we will experience a prolonged period of cooler weather.

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In a surprise discovery, astronomers using the Burst Alert Telescope aboard the Swift satellite learned that both supermassive black holes in galaxy Mrk 739¹ (yes, it has two) are actively feeding on material. (Check out the link for a cool vid of the galaxy.) Mrk 739 is a mere 425 million light-years from Earth, making it the second-closest active pair of supermassive black holes to Earth. (The first-closest is in galaxy NGC 6240.)

So, besides the sheer coolness of two supermassive black holes in a single galaxy, why do astronomers care about such objects? As it turns out, they are an important key to understanding galaxy evolution.

Nearly every galaxy, including our own Milky Way, harbors a supermassive black hole in its nucleus, but only a few percent of those black holes are observed to be actively feeding on significant amounts of gaseous and stellar material. Such systems are referred to as active galactic nuclei or AGN for short, and they are believed to be a temporary stage through which all galaxies harboring supermassive black holes pass. During this relatively brief active period, typically lasting ~50 million years, the gaseous material AGN feed on becomes superheated as it spirals down onto the black hole, causing AGN to shine very brightly. The intense brightness means these objects are often observable at very great distances, and therefore over a big range of cosmic history. This is why AGN are important probes of galaxy evolution.

Astronomers aren’t entirely sure what drives this material from the outskirts of the galaxy all the way down to the black hole, but it has been posited that galaxy interactions, including major mergers like the one shown below, are a likely mechanism.

What’s happening here is that the mutual gravitational tugging on gas orbiting in the galactic disks causes it to lose angular momentum and travel inward toward the nucleus of at least one galaxy, and possibly both, eventually reaching one or both of the black holes. If both black holes are active, the object is referred to as a binary AGN. As the hypothesis goes, such objects should be abundant but short-lived (in cosmic terms), lasting a few to tens of millions of years depending on the distance between the black holes. Eventually, the black holes spiral down to merge into a single, more massive black hole, and the two galaxies become a single, more massive galaxy.

It is a fact that galaxies frequently merge — there are several striking examples of this — but whether they are a major mechanism for creating AGN is another matter. I am a co-author on several papers involving searches for binary black holes, including binary AGN and recoiling black hole pairs, and I have been somewhat surprised by the relatively low frequency with which we observe genuine binary AGN  — about 100 times less than the predicted frequency. This implies: 1) the measurements needed to make such detections at large distances are so fine that we are not detecting the vast majority of such objects; or 2) perhaps the notion that mergers play a major role in creating AGN needs to be reconsidered.

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Until recently, our Earth-Moon system was thought to be a rare configuration — most moons in the Solar System are proportionally very small compared to the planets they orbit, but our Moon is proportionally large at about one-quarter the size of Earth. Now, results from a new computer simulation conducted by physicists in Zurich and Colorado indicate that such a configuration may be more common than previously thought.

Our Moon is believed to have formed 100 million years after the initial formation of the Solar System when a Mars-sized planet collided with Earth, breaking the smaller planet apart, and forming a debris ring that eventually coalesced into what is now the Moon. According to the simulations, there is about a one in 12 chance of a similar scenario occurring in other systems.

While interesting, keep in mind that these are simulations, not observations, and they do not take into account all of the different variables. They simply tell us that formation of other planets with proportionally large moons is plausible.

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