We may be already seeing the makings of next solar cycle, peeking out through the current one.
It’s been a wild ride. Thus far, Solar Cycle Number 25 has been one of the strongest cycles in recent memory, producing several massive sunspot groups. The current large region turned Earthward (Active Region 3780) is now easily visible with eclipse glasses… no magnification needed. Cycle 25 started back in 2019.
Massive sunspot rotates into view. Credit: NASA/SDO A Stormy YearTo be sure, the latest solar cycle will be one for the history books, as it heads towards an active maximum in 2025. But even though Cycle 25 will run out through the remainder of the current decade, there are already signs that Cycle 26 could be beginning, just under the roiling solar surface. A study out of the University of Birmingham recently presented at the Royal Astronomical Society’s National Astronomical Meeting in Hull (United Kingdom) shows that key indicators for the start of the next cycle may already be in place.
Numbering the solar cycle under current the convention goes all the way back to the start of Cycle 1 in 1755. The pattern for numbering cycles was started in 1852 by astronomer Rudolf Wolf.
We know that a new solar cycle has formally started when sunspots appear at higher solar latitudes. These also typically have a reversed polarity, versus the previous cycle. These then push down near the solar equator as the cycle progresses. Spot from two cycles can also mix as the transition gets underway.
A large sunspot group from May 2024. Credit: NASA/SDOLaying out spots from successive cycles versus latitude creates a butterfly diagram that demonstrates this effect, in what’s known as Spörer’s Law.
A butterfly graph (top) showing sunspots versus latitude over time. Credit: NASA/MSFC Peering Inside the SunBut there’s more to the Sun than meets the eye. As a large ball of hydrogen and helium gas, the Sun does not rotate as a single solid mass. Instead, it rotates faster at the equator (25 days) versus near the poles (34 days). Scientists can probe the solar interior via a method known as solar helioseismology, which looks at waves crossing the solar photosphere in an effort to model the interior.
These internal sound waves form bands in a phenomenon known as solar torsional oscillation. Faster-rotation belts appear as a harbinger of the next cycle. These move along with visible sunspots towards the solar equator as the cycle progresses.
“The indication of Cycle 26 that we see is that the solar rotation has been speeding up at around 50 degrees latitude and now appears to be leveling off,” Rachel Howe (University of Birmingham) told Universe Today. “This forms part of a pattern called the torsional oscillation, where bands of slightly faster and slower rotation emerge at mid-latitudes before the cycle officially starts and move down to lower latitudes, alongside the sunspot activity, as the cycle develops. In earlier cycles we have seen that the faster-rotating band associated with the cycle can be traced back to around the maximum of the previous cycle, and we think we’re seeing the beginning of the pattern again. It will still be several years before we can expect to see sunspots belonging to the new cycle, though!”
A solar cycle map, showing speed and torsional oscillations over time versus latitude for the last three solar cycles… and the start of Solar Cycle 26 (upper right). Credit: Rachel Howe. Monitoring the Sun Around the ClockThe Global Oscillation Network Group (GONG) makes the science of helioseismology possible. This is a worldwide network that monitors the Sun continuously. In space, the Helioseismic Magnetic Imager aboard the joint ESA/NASA Solar and Heliospheric Observatory (SOHO) compliments this effort. The Michelson Doppler Imager (MDI) on NASA’s Solar Dynamics Observatory (SDO) also plays a key role in this campaign. This effort goes back to 1995, spanning the last three solar cycles.
Big Bear Lake and Solar Observatory, part of the GONG network monitoring the Sun.This gives researchers a look at the start of the last two solar cycles. It also hints at what might be in store for the start of Solar Cycle 26. “If we can understand how this flow pattern relates to the sunspot cycle, we may be able to do better at predicting how strong the next solar maximum will be and when it will occur,” says Howe.
Sunspots from July 31st, 2024. Credit: Eliot Herman.Solar Cycle 25 has thus far been extremely active, far beyond expectations. This follows the historic lull that preceded it between Cycles 24 and 25. Observers saw few sunspots during this profound minimum. Still, this fell in line with many predictions made by astronomers who study the Sun, suggesting a stronger than usual cycle on rebound.
Looking Ahead to Cycle 26“The Sun is always surprising,” says Howe. “Some of the most exciting discoveries recently have come from the spacecraft—Solar Orbiter and Parker Solar Probe—that are flying closer to the Sun than ever before, helping scientists to unravel the connections between what we see on the Sun’s surface and the ‘space weather’ events that affect us on Earth. We’re looking at the surface of the Sun in more detail than ever before, but there’s also a place for long-term studies (which this work is a part of) that follow the large-scale patterns inside the Sun over decades.”
A magnetic view of the Sun, courtesy of SDO. Credit: NASA/SDOThe May 10th solar storm was thus far the most impressive one of the cycle. This storm sent aurora to latitudes far south as Spain and Mexico, areas where aurorae are rarely seen. We were treated to a persistent red glow watching from central Germany, an unforgettable sight.
Solar Cycles and MoreHistorically, the Wolf Sunspot Number defines the level of solar activity. Astronomers refer to this as the Relative or Zürich Sunspot Number. One 2013 study suggested that the orientation and strength of the heliospheric current sheet is a better indicator of the health of the current solar cycle, rather than the sunspot number.
We usually say it’s an 11-year solar cycle from one minima/maxima to the next… but it’s actually double that length. The Sun’s magnetic field flips every 11-years, returning to the same relative orientation every 22 years.
We see ‘starspot cycles’ on other suns as well. It is also unclear why an 11-year cycle is ‘baked in’ to our Sun. We’re also unsure if this has always been the case throughout its 4.6-billion year life span.
This research provides a great model to test the next solar cycle, as we struggle to understand and live with our tempestuous star.
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Scientists discovered the Andromeda galaxy, known as M31, hundreds of years ago, and around a century ago, we realized that it had negative radial velocity toward the Milky Way. In other words, eventually, the two galaxies would merge spectacularly. That has been common knowledge for astronomers since then, but is it really true? A new paper from researchers at the University of Helsinki looks at several confounding factors, including the gravitational influence of other galaxies in our local group, and finds only a 50% chance that the Milky Way will merge with the Andromeda galaxy in the next 10 billion years.
That seems like a pretty big thing to get the physics wrong on. So, how did the authors come to that conclusion? They accounted for a problem that has been popularized in media as of late – the three-body – or in this case, four-body – problem. And with that problem comes a lot of uncertainty, which is why there’s still a 50% chance that this huge event might still happen.
Thinking of Andromeda and the Milky Way in isolation doesn’t account for the other galaxies in what we know as the “Local Group.” This comprises approximately 100 smaller galaxies at various orientations, distances, and speeds. The largest of the remaining galaxies is the Triangulum galaxy, M33, which is about 2.7 million light-years away and consists of upwards of a mere 40 billion stars. That’s about 40% of the approximately 100 billion stars in the Milky Way but a mere 4% of the nearly 1 trillion stars estimated to exist in Andromeda. Still, they would have their own gravitational pull, contorting the simplistic dynamic between Andromeda and the Milky Way.
Fraser explains some of the orbital mechanics around Andromeda’s motion.Further confounding that dynamic is the Large Magellanic Cloud, which is either the second or third closest galaxy to our own at a distance of only 163,000 light years. This is slightly larger than the Milky Way’s diameter, at 105,700. It also houses around 20 billion stars, so while it’s even less massive than M33, it still exerts a hefty gravitational pull.
The authors accounted for the gravitational pull of both of those other galaxies in their calculations of the paths of the Milky Way and Andromeda over the next few billion years. They found that the complicated dance of astronomical giants could potentially result in a scenario where the two galaxies don’t merge. However, there was another significant factor in their calculations: uncertainty.
Scientists never like uncertainty. In fact, much of their research tries to place bounds on certain parameters, like the rotational speed of galaxies or the distances between them. Unfortunately, despite their proximity, there are many uncertainties surrounding the four galaxies used in the study, and those uncertainties make precise calculations of the effects of their gravitational and rotational pull difficult.
Fraser discusses what stars, if any, we can see in Andromeda.Developing estimates rather than concrete numbers is one-way scientists often deal with uncertainty, and in this case, that estimate fell right at the 50% mark in terms of whether or not the two galaxies would collide. However, there is still a lot of uncertainty in that estimate, and plenty more confounding factors, including the other galaxies in the local group, will influence the final outcome. Ultimately, time will help solve the mystery, but that is a very long time on the scale of galaxy mergers. If it happens at all, a merger between the Milky Way and Andromeda will happen long after our own Sun has burnt out, and humans will either die out with it or find a way to expand to new stars. And if, at that point, we get easy access to an additional galaxy’s worth of resources, it would be all the better for us.
Learn More:
Sawala et al. – Apocalypse When? No Certainty of a Milky Way — Andromeda Collision
UT – Are Andromeda and the Milky Way Already Exchanging Stars?
UT – What a Mess. When the Milky Way and Andromeda Merge, it’ll Look Like This
UT – We Might Be Able to Measure Dark Energy Through the Milky Way’s Collision With Andromeda
Lead Image:
This illustration shows a stage in the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy, as it will unfold over the next several billion years. In this image, representing Earth’s night sky in 3.75 billion years, Andromeda (left) fills the field of view and begins to distort the Milky Way with tidal pull.
Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger
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