Одон орон судлаачид тодорхойгүй хугацааны дараа бүрмөсөн алга болсон, давтамж бүхий радио дохиог бүртгэж авсан нь шинжлэх ухааны шинэ сорилт болж байна.
2022 оны тавдугаар сарын 14-нд Өмнөд Африкийн радио дурангаар Милкий Вэй галактикийн хавтгайн ойролцоогоос LPT J1555−5631 хэмээх сонирхолтой эх үүсвэрийг илрүүлжээ. Энэхүү биет нь 62.2 минутын давтамжтайгаар хоёр өөр төрлийн радио дохиог 15 цагийн турш тасралтгүй илгээсэн байна. Австралийн ASKAP дурангийн тусламжтайгаар тус дохиог баталгаажуулсан бөгөөд гол дохио нь 2.44 минут, харин богино дохио нь 0.66 минут үргэлжилж байв.
Скотт Хайманаар удирдуулсан эрдэмтдийн баг тус биетийг эргэлтийн тэнхлэг болон соронзон тэнхлэг нь бараг перпендикуляр байрлалтай “ортогональ эргэлдэгч” байх магадлалтай гэж үзжээ. Энэ нь соронзон туйлууд ээлжлэн дэлхий рүү чиглэснээр өөр өөр дохио үүсгэж буй хэрэг юм. Гэсэн хэдий ч дохионы хоорондох зай нь энгийн хоёр туйлт соронзон загварт бүрэн нийцэхгүй байгаа нь соронзон орон нь илүү төвөгтэй бүтэцтэй байж болзошгүйг харуулж байна.
MeerKAT болон ASKAP дурангийн архивын мэдээллээс санамсаргүйгээр олдсон энэ биетийг супернова дэлбэрэлтийн үлдэгдэл болох SNR G 326.3−1.8-ын ойролцоо байрлаж байгааг тогтоосон ч, зайнаас бусад шинж чанар нь тодорхойгүй хэвээр байна. Судлаачид сүүлийн таван жилийн хугацаанд тус бүс нутгийг олон удаа ажигласан боловч дахин нэг ч дохио бүртгэгдээгүй юм. Мөн рентген болон хэт улаан туяаны ажиглалтаар ямар нэгэн эх үүсвэр илрээгүй нь энэхүү үзэгдлийг улам бүр нууцлаг болгож байна.
Эрдэмтэд үүнийг нейтрон од эсвэл цагаан одой од байж магадгүй хэмээн таамаглаж байгаа ч аль аль нь ажиглагдсан шинж тэмдгүүдийг бүрэн тайлбарлаж чадахгүй байна. Энэ төрлийн “урт хугацаат транзиент” (LPT) объектууд нь богино хугацаанд идэвхжиж, дараа нь удаан хугацаагаар чимээгүй болдог онцлогтой. Үүнтэй төстэй үзэгдэл өмнө нь бүртгэгдэж байсан ч, эдгээр биетийн мөн чанар болон тэдгээр нь нэг төрлийн объект мөн эсэх нь одоогоор шинжлэх ухааны нээлттэй асуулт хэвээр үлджээ.
Дэлгэрэнгүйг эх сурвалжаас харах
↓Эх сурвалжийг нээх ↓
On May 14, 2022, a radio telescope in South Africa caught something flickering near the crowded plane of the Milky Way. First came a long pulse, then a short, sharper one, and then nothing for an hour, until the pattern started over exactly on time.
It kept that rhythm for about 15 hours. Then it stopped. Telescopes have gone back to the same patch of sky again and again for more than five years, and they haven’t heard a single pulse since.
A Double Heartbeat Every 62 Minutes
The source now has a catalog name, LPT J1555−5631, and a precise beat. It pulsed every 62.2 minutes, a period confirmed by a 10-hour observation with Australia’s ASKAP telescope. That makes it one of the long-period transients, a recently recognized and baffling class of objects that send out long radio bursts separated by long, regular silences.
Even among those oddballs, this one stands out. Each cycle carried two distinct pulses rather than one, with one lasting longer than the other, according to ScienceAlert. The main pulse lasted about 2.44 minutes, and the narrower interpulse lasted about 0.66 minutes. Even so, both reached almost the same peak brightness.
The two pulses also spun in opposite directions. Radio waves can carry a corkscrew twist called circular polarization, turning either clockwise or counterclockwise, and the two pulses here turned opposite ways. The shorter pulse was almost entirely circularly polarized, as if it came from a completely different part of the object.
That’s very likely what happened. The team, led by Scott Hyman of Sweet Briar College, concluded in The Astrophysical Journal that the object is a near-orthogonal rotator. Its spin axis and magnetic axis are almost perpendicular, so both magnetic poles sweep past Earth once per rotation. One pole produces the long pulse, and the other produces the short one.
The spacing doesn’t quite fit, though. The pulses were 165.4 degrees apart, not the neat 180 degrees a simple two-pole magnet would give. Hyman told ScienceAlert that this offset is an important clue that the magnetic field is more tangled than a simple bar magnet.
Found by Accident in an Old Archive
No one was looking for this object when it appeared. The team stumbled on it while searching a public MeerKAT archive of supernova remnant observations for something else entirely. It turned up in data that had been sitting there since the day it was recorded.
Luck had already played its part. On the same day as the MeerKAT observation, Australia’s ASKAP telescope was surveying that region and caught the same source. Two observatories on two continents had recorded the same short-lived signal without anyone realizing it.
The location only deepens the puzzle. The source lies about 0.5 degrees from the center of a supernova remnant called SNR G 326.3–1.8, the expanding shell of debris from an exploded star. Its distance is much less certain. The best figure is about 5.4 kiloparsecs, roughly 17,600 light-years, and even the authors call that estimate weak.
Five Years of Silence
Once the team knew what to look for, they went back through every record they could find. They turned up about 60 ASKAP observations of the area between 2019 and 2026, and only the May 2022 one contains pulses. Eleven MeerKAT observations from a 2021 survey of the galactic plane show nothing, and neither do two from 2019. Australia’s Murchison Widefield Array looked in June 2022, just weeks after the outburst, and found only silence.
That leaves a strangely narrow life span. Based on the gaps between observations, the object was active for at least 15 hours and at most 10 months.
Other wavelengths turned up nothing as well. The X-ray catalogs from eROSITA, XMM-Newton and Chandra show no source at that spot. The closest visible star lies about 1 arcsecond away, but the field is so crowded that the overlap is probably chance. Infrared surveys came up empty.
Two Suspects, Neither a Clean Fit
Two main suspects remain. A neutron star is the obvious first guess, but a 62-minute spin is far too slow for normal pulsar emission. To produce these pulses, its magnetic field would have to be heavily twisted or unusually complex.
A white dwarf has its own problem. No isolated white dwarf has ever been seen producing this kind of radio emission, so it would need a companion star, and none has turned up. The 62.2-minute spin is also shorter than the roughly 78-minute minimum orbit for the most common type of white dwarf binary.
Questions like these have followed the whole class from the start. GLEAM-X J1627−5235, observed in 2018 and reported in 2022, established the category, and around a dozen more have been found across the Milky Way since then. “Are all LPTs one type of object?” Hyman asked in his ScienceAlert interview, and the new paper leaves that question open.
Hyman has watched a signal disappear like this once before. In September 2002, he recorded GCRT J1745−3009, which produced five radio flares 77 minutes apart and then went silent. He searched for years without finding another and eventually moved on. That source has since flared up again, and two other vanished signals have done the same.
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