Strange Radiation From the Sun

  1. How do they know that powerful beams of certain particles, including X-rays are coming from the sun until they actually get here? They have been predicting this radiation for almos a week now! There must have been some beams of particles that came first and were somehow able to announce that some other particles were coming next! 2) Also are X-rays photons or something else?
  2. What other certain particles are coming besides X-rays, if so. Are gamma rays involved and are they photons? Will neutrinos bombard too?
    4( They said we would see the aurora borealis a lot due to this attack from the sun. This makes me wonder if there is an aurora austalialis or whatever they would call a south pole aurora borealis.
    5)Finally, is this radiation coming (in about an hour and a half from now) or what came the other day all coming out in a big huge sphere from the whole sun or is it in the form of a gigantic flare pointed toward only the earth?

IANAAstronomer, but here is my understanding…

  1. Astronomers know that certain visible events on the sun (like solar flares and such) are usually accompanied by particle emissions. So, when they see such an event they expect the particle storm to follow.

  2. Yes, x-rays are photons. They have a higher frequency than visible light. Gamma rays are also photons with even higher frequency.

  3. From what I understand the majority of the “storm” is composed of electrons. These electrons are moving at about a million miles an hour and so take about 3-4 days to reach the Earth. Visible light (and other photons like x-rays and gamma rays) of course travels at the speed of light and so gets here in about 10 minutes.

  4. Yes, there is an equivilent to the aurora borealis in the southern hemisphere.

  5. The energy storm is coming from a certain spot on the sun associated with a flare or something similar.

Solar flares and CMEs (coronal mass ejections) occur on “active regions” on the sun, which are usually centered around sunspots. They appear are bright in X-ray images. If a particularly large active region forms on the sun, you can be fairly certain that a big flare is going to happen within a few days. But it’s by no means a definite prediction, just a forecast of how likely a flare is.

When a flare does happen, it emits a burst of electromagnetic radiation ranging from radio to X-rays, and often gamma rays. These all travel at the speed of light (they are light) so we don’t get any advance warning at all. It lasts anywhere from several minutes to many hours. They can be dangerous to astronauts, but other than that there is no danger or even an indication.

A solar flare usually produces a coronal mass ejection (CME), which is basically a huge gust of solar wind, a big cloud of charged particles ejected at a high speed. It takes one or two days to get to earth, so we can see it coming. It’s not coming out in a spherical shell but as a cloud directed at a particular direction. If it hits the earth’s magnetosphere, it disrupts the earth’s magnetic field and can cause damage to power lines and other facilities. Some of the particles get past the magnetic field and impact the atmosphere, creating an aurora display. Most of it happens at the poles because charged particles tend to travel along magnetic field lines, not across.

Currently the best instrument for observing these CMEs is the LASCO coronagraph on the SOHO satellite. If you go to the latest SOHO images page and click on “more LASCO C3”, you should see that starting at the 10/28 11:42 image, you can see an expanding halo-like structure. This is a “halo CME” and it means the cloud of charged particles is headed directly towards us. There’s also a movie on this page.

A nitpick, but…

This isn’t strictly true. X-rays are photons from an atomic process, and gammas come from a nuclear process, so it’s possible that you can have X-rays of higher energy than gamma rays, though for the majority of incidents gammas will have the higher energy.

Nitpicking the nitpick…

In astronomical terms photon energy is the discriminating factor between X-rays and gamma rays. X-ray satellites, such as Chandra and XMM-Newton generally have a high energy cut-off that isn’t seen in the newer gamma ray satellites such as Integral.

Chandra has a high energy cut-off of about 10keV, and XMM-Newton of about 12keV. Integral has an energy range from 20keV to 80MeV. As you can see, the X-ray missions are designed to detect far lower energies than the gamma ray missions. Therefore, from an astrophyiscist’s point of view, a gamma ray and a X-ray, are two different fields of study.

For the record, I am a X-ray (and radio) astronomer.

And just to complete the OPs questions - neutrinos are bombarding us now and always in enormous numbers. I don’t believe they vary because of flares, however.

OK, maybe I’m a bit confused. I was going by the classic EM spectrum where things progress from infrared and visible light through ultraviolet and radio up to microwave and x-rays and finally to gamma rays. Here is an example of the view of things I am familiar with and that is the way I understood it from my electromagnetics classes.

Now, maybe I’ve forgotten a few things (it has been a while since electromag…) but wouldn’t a photon of a particular wavelength be defined the same way, regardless of the process that produced it? Or am I trying to compare apples and elephants here?

Doh! And, yes, I know the order is radio, microwave, infrared, visible, ultraviolet, x-ray, gamma ray. I really do. (Sigh)

Usually, astronomers call 1 MeV the cutoff between X-ray and gamma ray. That’s fine, though a bit arbitrary. If it were about half that-- specifically, 511 keV-- then it would be the energy released when an electron and positron annihilate each other. :slight_smile:

By the way, we are discussing the huge solar event on my Bulletin Board. It’s linked from my main page (and will migrate to the What’s New section in a few days, when this all dies down).

A nitpick:
When an electron and positron annihilate you get 1.022 MeV, in the form of two 511 KeV photons.

I made this mistake in the presence of one of the local solar physicists, and got rather berated for it. I’ll admit that I’m still unclear on the distinction, but apparently flares and CMEs are unrelated. What’s currently headed our way (or passed us) is a CME, not a flare.

Apples and elephants, sort of. X-rays have no upper bound for their energy. click here

It isn’t an unreasonable thing to make an arbitrary energy division, but the division between X and gamma is process rather than energy, unlike the other divisions.

Astronomers have their own peculiar terminology. To an astronomer, oxygen is a metal (all elements except hydrogen and helium are called metals).

There is a lot of exposition on this subject at Space Weather Dot Com.

The terms refer to different observable phenomena which may or may not be caused by the same basic mechanism. Different symptoms of the same disease, so to speak.

“Flare” refers to the intense burst of radiation, apparently a direct result of particle acceleration. Charged particles somehow get accelerated to hundreds of keV which interacts with plasma and magnetic waves to emit hard X-ray and radio waves. This also heats local plasma to tens of millions of degrees, which emits soft X-rays, UV and radio. Basically when you see a big spike on the GOES X-ray monitor we call it a flare.

CME refers to the ejectio of matter into interplanetary space. When we look at a coronagraph and see stuff being ejected, we call that a CME.

There are many flares that do not have observable CMEs associated with it. The opposite - CME without flare - is much less common, but it a few such cases have been reported. We still don’t understand the underlying mechanism of either phenomenon, let alone how the two are connected. (That is, we still can’t agree on one model.)

p.s. I agree that in astronomy, > 1 MeV range is usually called gamma rays regardless of emission mechanism. Often we don’t even know the emission mechanism, and it’s awkward to refer to your data as “X-ray and/or gamma ray” all the time. Anything between 10 keV and 1 MeV is “hard X-ray” and what Chandra, XMM etc. observe (0.1 to 10 keV, roughly) is “soft X-ray.”